DEVELOPMENT OF THE NATURAL SYSTEM UNDER THE INFLUENCE OF THE DOGMA OF
THE CONSTANCY OF SPECIES.
1759-1850.
From the year 1750 Linnaeus’ terminology of the organs of plants
and his binary method of naming species came into general use; the
opposition which his doctrines had till then encountered by degrees
died away, and if all that he taught was not universally accepted,
his treatment of the art of describing plants soon became the common
property of all botanists.
But in course of time two very different tendencies were developed;
most of the German, English, and Swedish botanists adhered strictly to
Linnaeus’ dictum, that the merit of a botanist was to be judged by the
number of species with which he was acquainted; they accepted Linnaeus’
sexual system as one that completed the science in every respect; they
thought that botany had reached its culminating point in Linnaeus, and
that any improvement or addition could only be made in details, by
continuing to smooth over some unevennesses in the system, to collect
new species and describe them. The inevitable result was that botany
ceased to be a science; even the describing of plants which Linnaeus
had raised to an art became once more loose and negligent in the hands
of such successors; in place of the morphological examination of the
parts of plants there was an endless accumulating of technical terms
devoid of depth of scientific meaning, till at length a text-book of
botany came to look more like a Latin dictionary than a scientific
treatise. In proof of this we may appeal to Bernhardi’s ‘Handbuch
der Botanik,’ published at Erfurt in 1804, and Bernhardi was one of
the best representatives of German botany of the time. How botany,
especially in Germany, gradually degenerated under the influence of
Linnaeus’ authority into an easy-going insipid dilettantism may very
well be seen from the botanical periodical, entitled ‘Flora,’ the first
volumes of which cover the greater part of the first fifty years of the
19th century; it is scarcely conceivable how men of some cultivation
could occupy themselves with such worthless matter. It would be quite
lost labour to give any detailed account of this kind of scientific
life, if it can be so called, this dull occupation of plant-collectors,
who called themselves systematists, in entire contravention of the
meaning of the word. It is true indeed that these adherents of Linnaeus
did some service to botany by searching the floras of Europe and of
other quarters of the globe, but they left it to others to turn to
scientific account the material which they collected.
But before this evil had spread very widely, a new direction to the
study of systematic botany and morphology was given in France, where
the sexual system had never met with great acceptance. Bernard de
Jussieu and his nephew, Antoine Laurent de Jussieu, taking up Linnaeus’
profounder and properly scientific efforts, made the working out of the
natural system, in Linnaeus’ own opinion the highest aim of botany, the
task of their lives. Here more was needed than a perpetual repetition
of descriptions of single plants after a fixed pattern; more exact
inquiries into the organisation of plants, and especially of the parts
of the fructification, must supply the foundation of larger natural
groups. It was a question therefore of new inductive investigation,
of real physical science, of penetrating into the secrets of organic
form, whereas the botanists who confined themselves to Linnaeus’ art of
description made no new discoveries respecting the nature of plants.
And if these men held to the dictum just quoted from Linnaeus, and
therefore regarded themselves as his genuine disciples, the founders
of the natural system had as good a right to the title, not because
they followed his nomenclature and method of diagnosis, but because
they strove after exactly that object which he had placed first in the
science, the construction of the natural system; they were really the
men whom he had meant when he spoke of ‘methodici’ and ‘systematici.’
The German, English, and Swedish collectors of plants adhered to the
less profound, every-day, practical precepts of their master; the
founders of the natural system followed the deeper traces of his
knowledge. This direction proved to be the only one endowed with living
power, the true possessor of the future.
The efforts of Jussieu, Joseph Gärtner, De Candolle, Robert Brown, and
their successors up to Endlicher and Lindley, are not marked only by
the fact that they did truly seek to exhibit the gradations of natural
affinities by means of the natural system; equally characteristic
of these men is their firm belief in the dogma of the constancy of
species as defined by Linnaeus. Here at once was a hindrance to their
efforts; the idea of natural relationship, on which the natural system
exclusively rests, necessarily remained a mystery to all who believed
in the constancy of species; no scientific meaning could be connected
with this mysterious conception; and yet the farther the inquiry
into affinities proceeded, the more clearly were all the relations
brought out, which connect together species, genera, and families.
Pyrame de Candolle developed with great clearness a long series of
such affinities as revealed to us by comparative morphology, but how
were these to be understood, so long as the dogma of the constancy
of species severed every real objective connection between two
related organisms? Little indeed could be made of these acknowledged
affinities; still, in order to be able to speak of them and describe
them, recourse was had to indefinite expressions, to which arbitrary
and figurative meanings could be assigned. Where Linnaeus had spoken
of a class-plant or generic plant, the expression ‘plan of symmetry’ or
‘type’ was used, meaning an ideal original form, from which numerous
related forms might be derived. It was left undecided, whether this
ideal form ever really existed, or whether it was merely the result
of intellectual abstraction; and thus the forms of thought of the
old philosophy soon began to reappear. The Platonic ideas, though
mere abstractions and therefore only products of the understanding,
had been regarded not only by the school of Plato, but also by the
so-called Realists among the schoolmen, as really existing things. The
systematists obtained the idea of a type by abstraction, and the next
step was easy, to ascribe with the Platonists an objective existence to
this creature of thought, and to conceive of the type in the sense of a
Platonic idea. This was the only view that was possible in combination
with the dogma of the constancy of species, and so Elias Fries, in
his ‘Corpus Florarum,’ 1835, in speaking of the natural system, could
consistently say, ‘est quoddam supranaturale,’ and maintain that each
division of it ‘ideam quandam exponit.’ So long as the constancy of
species is maintained, there is no escaping from the conclusion drawn
by Fries, but it is equally certain that systematic botany at the
same time ceases to be a scientific account of nature. Systematists,
adopting this conclusion as necessarily following from the dogma,
might consider themselves as seeking to express in the natural system
the plan of creation, the thought of the Creator himself; but in this
way systematic botany became mixed up with theological notions, and
it is easy to understand why the first feeble attempts at a theory of
descent encountered such obstinate, nay, fanatical opposition from
professed systematists, who looked upon the system as something above
nature, a component part of their religion. And if we look back we find
that these views are based on the dogma of the constancy of species,
while Linnaeus’ ‘Philosophia Botanica’ teaches us on what grounds this
dogma rests, where it says, ‘Novas species dari in vegetabilibus
negat generatio continuata, propagatio, observationes quotidianae,
cotyledones.’
In spite of all this one important advance was made by the successors
of Jussieu; the larger groups of genera, the families, were defined
with the certainty and precision, with which Linnaeus had fixed the
boundaries of species and genera, and were supplied with characteristic
marks. They succeeded also in clearly distinguishing various still
larger groups founded on natural affinity, such as the Monocotyledons
and Dicotyledons; the distinction between Cryptogams and Phanerogams
was by degrees better appreciated, though this point could not be
finally settled, so long as it was attempted to reduce the Cryptogams
entirely to the scheme of the Phanerogams. The chief hindrance however
to the advance of systematic botany, at least at the beginning of
this period, lay in the defective morphology enshrined in Linnaeus’
terminology and in his doctrine of metamorphosis. A great improvement
certainly was effected in the early part of the 19th century by De
Candolle’s doctrine of the symmetry of plants,—a doctrine which has
been much undervalued, and that merely on account of its name; it is
really a comparative morphology, and the first serious attempt of the
kind since the time of Jung that has produced any great results; a
series of the most important morphological truths, with which every
botanist is now conversant, were taught for the first time in De
Candolle’s doctrine of symmetry in 1813. But one thing was wanting
not only in Jussieu and De Candolle, but in all the systematists of
this period, with the single exception of Robert Brown, and this
was the history of development. The history of the morphology and
systematic botany of this period shows indeed, that the comparison of
mature forms leads to the recognition of many and highly important
morphological facts; but as long as matured organisms only are
compared, the morphological consideration of them is always disturbed
by the circumstance that the organs to be compared are already adapted
to definite physiological functions, and thus their true morphological
character is often entirely obscured; on the other hand, the younger
the organs are, the less is this difficulty experienced, and this is
the real reason why the history of development is of so great service
to morphology. It was then one of the characteristic features of the
period we are describing, that its morphology was formed upon the study
of matured forms; the history of development, or at all events of very
early stages of development, could not be turned to account till after
1840, for skill in the use of the microscope, here indispensable, was
not sufficiently advanced before that time to make it possible to
follow the growth of organs from their first beginnings.
The establishment of natural affinities combined with the assumption of
the constancy of species, the growth of comparative morphology without
the history of development, lastly, the very subordinate attention
still paid to the Cryptogams,—these are the special characteristics of
the period which has now to be described at greater length.
* * * * *
Here we must once more call attention to the fact, that Linnaeus was
the first to perceive that a system which was to be the expression
of natural affinities could not be attained in the way pursued by
Cesalpino and his immediate successors. All who have attentively
studied the writings of Linnaeus which appeared after the ‘Classes
Plantarum’ (1738) must have seen the difference between that way and
the one recommended by him—a difference which is the more obvious
because Linnaeus himself, like his predecessors, constructed an
artificial system on predetermined principles of classification, and
always employed it for practical purposes, while he published at the
same time in the above-named work his fragment of a natural system,
and in the preface set forth the peculiar features of the natural and
artificial systems in striking contrast with one another. The first
thing and the last, he says in his prefatory remarks to his fragment,
which is demanded in systematic botany, is the natural method, which
slighted by less learned botanists has always been highly regarded by
the more sagacious, and has not yet been discovered. If, he continues,
we collect the natural orders from all existing systems (up to 1738),
we shall get but a small list of really allied plants, though so many
systems have claimed to be natural. He had himself long laboured
to discover the natural method and had found out some things that
were new; but though he had not succeeded in carrying it through to
a perfect work, he would continue his efforts as long as his life
lasted. He makes the very important remark, that a key, that is, _a
priori_ principles of classification, cannot be given for the natural
method, till all plants have been reduced to orders; that for this
no _a priori_ rule is of value, neither this nor that part of the
fructification, but the simple symmetry alone (simplex symmetria) of
all the parts, which is often indicated by special marks. He suggests
to those who are bent on trying to find a key to the natural system,
that nothing has more general value than relative position, especially
in the seed, and in the seed especially the ‘punctum vegetans,’—a
distinct reference to Cesalpino. He says that he establishes no classes
himself, but only orders; if these are once obtained, it will be easy
to discover the classes. The essence of the natural system could not
have been more clearly expounded in Linnaeus’ time, than it is in
these sentences. He established as early as 1738 sixty-five natural
orders, which he at first simply numbered; but in the first edition
of the ‘Philosophia Botanica’ in 1751, where the list is increased to
sixty-seven, he gave a special name to each group; and he showed his
judgment by either taking his names from really characteristic marks,
or what was still better, by selecting a genus and so modifying its
name as to make it serve as a general term for a whole group. Many of
these designations are still in use, though the extent and content
of the groups have been greatly changed. This mode of naming is an
important point, because it expresses the idea, that the different
genera of such a group are to some extent regarded as forms derived
from the one selected to supply the name. Many of Linnaeus’ orders
do in fact indicate cycles of natural affinity, though single genera
are not unfrequently found to occupy a false position; at all events,
Linnaeus’ fragment is much the most natural system proposed up to 1738,
or even to 1751. It is distinguished from Kaspar Bauhin’s enumeration
in this, that its groups do not run into one another, but are defined
by strict boundaries and fixed by names.
The Linnaean list is distinctly marked by the endeavour to make first
the Monocotyledons, then the Dicotyledons, and finally the Cryptogams
follow one another; that the old division into trees and herbs already
rejected by Jung and Bachmann, but still maintained by Tournefort and
Ray, disappears in Linnaeus’ natural system will be taken for granted
after what has been already said of it, and from this time forward this
ancient mistake is banished for ever.
In BERNARD DE JUSSIEU’S[34] arrangement of 1759 we find some
improvements in the naming, the grouping, and the succession, but at
the same time some striking offences against natural affinity. He
published no theoretical remarks on the system, but gave expression
to his views on relations of affinity in the vegetable kingdom in
laying out the plants in the royal garden of Trianon, and in the
garden-catalogue. His nephew published his uncle’s enumeration in the
year 1789 in his ‘Genera Plantarum,’ affixing the date of 1759 given
above. The difference between it and the Linnaean fragment does not
seem sufficiently marked to make it necessary to reproduce it here.
It should be noticed however that Jussieu begins with the Cryptogams,
passes through the Monocotyledons to the Dicotyledons, and ends with
the Conifers. Adanson’s claims of priority over Bernard de Jussieu
(see the ‘Histoire de la Botanique’ de Michel Adanson, Paris, 1864,
p. 36) may be passed over as unimportant. The natural system was not
advanced by Adanson to any noticeable extent; how little he saw into
its real nature and into the true method of research in this department
of botany is sufficiently shown by the fact, that he framed no less
than sixty-five different artificial systems founded on single marks,
supposing that natural affinities would come out of themselves as
an ultimate product,—an effort all the more superfluous, because a
consideration of the systems proposed since Cesalpino’s time would have
been enough to show the uselessness of such a proceeding.
The first great advance in the natural system is due to ANTOINE LAURENT
DE JUSSIEU[35] (1748-1836). After all that has been said no further
proof is needed that he was no more the discoverer or founder of the
natural system than his uncle before him. His real merit consists in
this, that he was the first who assigned characters to the smaller
groups, which we should now call families, but which he called orders.
It is not uninteresting to note here how Bauhin first provided the
species with characters, and named the genera but did not characterise
them, how Tournefort next defined the limits of the genera, how
Linnaeus grouped the genera together, and simply named these groups
without assigning to them characteristic marks, and how finally Antoine
Laurent de Jussieu supplied characters to the families which were now
fairly recognised. Thus botanists learnt by degrees to abstract the
common marks from like forms; the groups thus constituted were being
constantly enlarged, and an inductive process was thus completed which
proceeded from the individual to the more general.
It might appear that the merit of Antoine de Jussieu is rated too low,
when we praise him chiefly and simply for providing the families with
characters; but this praise will not seem small to those who know the
difficulty of such a task; very careful and long-continued researches
were necessary to discover what marks are the common property of a
natural group. Jussieu’s numerous monographs show with what earnestness
he addressed himself to the task; and it must be added, that he was
not content simply to adopt the families established by Linnaeus and
by his uncle and the limits which they had assigned to them, but
that he corrected their boundaries and in so doing established many
new families, and was the first who attempted to distribute these
into larger groups, which he named classes. But in this he was not
successful. His attempt to exhibit the whole vegetable kingdom in all
its main divisions, to unite the classes themselves into higher groups,
was also unsuccessful, for these larger divisions remained evidently
artificial. The three largest groups on the contrary, into which he
first divides the world of plants, the Acotyledons, Monocotyledons, and
Dicotyledons are natural; but they had been already partly marked out
by Ray, afterwards by Linnaeus, and finally in Bernard de Jussieu’s
enumerations. Still it is the younger Jussieu’s great and abiding
merit, to have first attempted to substitute a real division of the
whole vegetable kingdom into larger and gradually subordinate groups
for mere enumerations of smaller co-ordinated groups,—an undertaking
which Linnaeus expressly declared to be beyond his powers. If then
Jussieu’s system was far from giving a satisfactory insight into
the affinities of the great divisions of the vegetable kingdom, yet
it opened out many important points of view, from which they could
afterwards be discovered, and it certainly became the foundation for
all further advance in the natural method of classification; for this
reason it is necessary to give a view of it in the following table:—
A. L. de Jussieu’s System of 1789.
CLASS.
Acotyledones I.
{ Stamina hypogyna II.
Monocotyledones { perigyna III.
{ epigyna IV.
{ { Stamina epigyna V.
{ Apetalae { perigyna VI.
{ { hypogyna VII.
{ { Corolla hypogyna VIII.
{ Monopetalae{ perigyna IX.
Dicotyledones.{ { epigyna { antheris connatis X.
{ { { distinctis XI.
{ { Stamina epigyna XII.
{ Polypetalae{ hypogyna XIII.
{ { perigyna XIV.
{ Diclines irregulares XV.
This table shows that Jussieu did not oppose the Cryptogams, which
he calls Acotyledones, to the whole body of Phanerogams, as Ray did
under the name of Imperfectae; he rather regards the Acotyledones as
a class co-ordinate with the Monocotyledones and Dicotyledones; but
this mistake or similar mistaken views run through all systematic
botany up to 1840; the morphology founded by Nägeli and by Hofmeister’s
embryological investigations first showed that the Cryptogams separate
into several divisions, which co-ordinate with the Monocotyledons
and Dicotyledons. At the same time the use of the word Acotyledones
for Linnaeus’ Cryptogams shows that Jussieu overrated the systematic
value of the cotyledons, because, as is seen from the introduction
to his ‘Genera Plantarum,’ he was quite in the dark on the subject
of the great difference between the spores of Cryptogamic plants and
the seeds of Phanerogams. His conception of the organs of generation
was essentially that of Linnaeus; hence he judged of the Cryptogams
according to the scheme of the Phanerogams, and, not perceiving their
peculiarities, he virtually characterised them by negative marks.
If we notice in the above table how the Phanerogams are separated
into classes, it strikes us that the triple division into hypogynous,
perigynous, and epigynous is repeated no less than four times; this
shows that Jussieu had mistaken ideas of the value of these marks for
classification, whereas the recurrence of them so often should of
itself have suggested a doubt on this point. To judge of his system
more exactly we must here give his series of the families, which he had
already raised to the number of a hundred.
Class I.
1. Fungi.
2. Algae.
3. Hepaticae.
4. Musci.
5. Filices.
6. Naiades.
Class II.
7. Aroideae.
8. Typhae.
9. Cyperoideae.
10. Gramineae.
Class III.
11. Palmae.
12. Asparagi.
13. Junci.
14. Lilia.
15. Bromeliae.
16. Asphodeli.
17. Narcissi.
18. Irides.
Class IV.
19. Musae.
20. Cannae.
21. Orchides.
22. Hydrocharides.
Class V.
23. Aristolochiae.
Class VI.
24. Elaeagni.
25. Thymeleae.
26. Proteae.
27. Lauri.
28. Polygoneae.
29. Atriplices.
Class VII.
30. Amaranthi.
31. Plantagines.
32. Nyctagines.
33. Plumbagines.
Class VIII.
34. Lysimachiae.
35. Pediculares.
36. Acanthi.
37. Jasmineae.
38. Vitices.
39. Labiatae.
40. Scrophulariae.
41. Solaneae.
42. Borragineae.
43. Convolvuli.
44. Polemonia.
45. Bignoniae.
46. Gentianeae.
47. Apocyneae.
48. Sapotae.
Class IX.
49. Guajacanae.
50. Rhododendra.
51. Ericae.
52. Campanulaceae.
Class X.
53. Cichoraceae.
54. Cinarocephalae.
55. Corymbiferae.
Class XI.
56. Dipsaceae.
57. Rubiaceae.
58. Caprifolia.
Class XII.
59. Araliae.
60. Umbelliferae.
Class XIII.
61. Ranunculaceae.
62. Papaveraceae.
63. Cruciferae.
64. Capparides.
65. Sapindi.
66. Acera.
67. Malpighiae.
68. Hyperica.
69. Guttiferae.
70. Aurantia.
71. Meliae.
72. Vites.
73. Gerania.
74. Malvaceae.
75. Magnoliae.
76. Anonae.
77. Menisperma.
78. Berberides.
79. Tiliaceae.
80. Cisti.
81. Rutaceae.
82. Caryophylleae.
Class XIV.
83. Sempervivae.
84. Saxifragae.
85. Cacti.
86. Portulaceae.
87. Ficoideae.
88. Onagrae.
89. Myrti.
90. Melastomae.
91. Salicariae.
92. Rosaceae.
93. Leguminosae.
94. Terebinthaceae.
95. Rhamni.
Class XV.
96. Euphorbiae.
97. Cucurbitaceae.
98. Urticae.
99. Amentaceae.
100. Coniferae.
Jussieu’s division of the Cryptogams and Monocotyledons offers much
that is satisfactory, if we put the position of the Naiades out of
sight. The grouping of the Dicotyledons on the contrary is to a great
extent unsuccessful, chiefly owing to the too great importance which
he attached to the insertion of the parts of the flowers, that is, to
the hypogynous, perigynous, and epigynous arrangement. It is in this
grouping of families into classes that the weak side of the system
lies; it is utterly artificial, and the task of his successors has been
to arrange the families of the Phanerogams, which were most of them
well-established, and especially those of the Dicotyledons, in larger
natural groups. But this could not be effected, till morphology opened
new points of view for systematic botany; Jussieu, as has been already
remarked, accepted Linnaeus’ views of the morphology of the organs of
fructification in Phanerogams, though he introduced many improvements
in details. He laid greater stress on the number and relative positions
of the different parts of the flower; attention to their insertion on
the flowering axis, which he designated as hypogynous, perigynous,
and epigynous, would have been a great step in advance, if he had not
overrated its systematic value. The morphology of the fruit is very
superficial in Jussieu; even the designation of dry indehiscent fruits
as naked seeds recurs in his definitions, though as it happens this
misconception does not cause any great disturbance. How inexact was his
investigation of the organs of fructification, when they were somewhat
small and obscure, is best shown by the fact that the Naiades, which
are made to include Hippuris, Chara, and Callitriche, appear among the
Acotyledons, and that Lemna and the Cycads are placed with the Ferns.
Jussieu explained the dictum, ‘Natura non facit saltus,’ to mean that
the whole body of plants in its natural arrangement must exhibit a
lineal series ascending from the most imperfect to the highest forms;
but he does not say whether Linnaeus’ comparison of the natural system
to a geographical map, the countries in which answer to orders and
classes, is also admissible.
His theoretical observations on the value to be given to certain marks
in a systematic point of view are not attractive, and for the most
part not very correct; he speaks as though some marks must have a
more extensive, others a less extensive value; the perception of the
fact, so far as it is true, rests entirely upon induction; that is,
after the natural affinities have been already recognised to a certain
extent, it becomes apparent that certain marks remain constant in
larger or smaller groups; the systematist can now go on to try whether
such constant marks occur in other plants also, which he had hitherto
assigned to other groups, and thus put it to the test whether those
marks may not be accompanied by others, which would serve to establish
the affinities; that Jussieu did so proceed in defining his families
admits of no doubt, but he was not himself thoroughly conscious of the
fact; at all events, he did not extend this mode of proceeding, the
seeking after leading marks, to the establishing of larger groups or
classes, for these he founded on predetermined principles.
Jussieu’s labours as a systematist were not confined to the publication
of his ‘Genera Plantarum’; on the contrary, his most fruitful
researches began after 1802, and were continued to the year 1820, and
their results appeared in a long series of monographs on different
families in the Mémoires du Museum. He felt with De Candolle, Robert
Brown, and later systematists, that the perfecting of the natural
system depended mainly on the careful establishing and defining of
families. His efforts received a new impulse from the work of a German
writer, whose first volume had appeared in 1788, a year therefore
before the ‘Genera Plantarum,’ a second following it in 1791, and a
supplementary volume in 1805.
This work was JOSEPH GÄRTNER’S[36] ‘De fructibus et seminibus
plantarum,’ in which the fruits and seeds of more than a thousand
species are described and carefully figured. But almost more important
than these numerous descriptions, though they offered rich material
to the professed systematists, were the introductions to the first
two volumes, and especially to those of 1788. They contain valuable
reflections on sexuality in plants,—a subject which had remained in
the condition in which it was left by Camerarius (1694) till it was
greatly developed by Koelreuter after 1761, and had since then been
little studied,—and an account of the morphology of fruits and seeds,
the knowledge of which had gone back rather than advanced since the
days of Malpighi and Grew. Gärtner was well qualified for this work by
his unparalleled knowledge of the forms of fruits, and still more by
the character of his mind. Free from Linnaeus’ scholastic bias, he
addressed himself to the examination of the most difficult organs of
plants with as great freedom from prepossessions as exact acquaintance
with the writings of others; he gives us the impression of a modern man
of science more than any other botanist of the 18th century, with the
exception of Koelreuter. He knew how to communicate with clearness of
language and perspicuity of arrangement whatever he gathered of general
importance from each investigation. Though it is easy to see that the
founding of the natural system was ever before his mind as the final
object of his protracted labours, he was in no eager haste to reach it;
he contented himself with arranging his fruits, saying expressly that
the natural system would never be founded by these means alone, though
the exact knowledge of fruits and seeds supplied the most important
means for decision. Thus his great work was at once an inexhaustible
mine of single well-ascertained facts, and a guide to the morphology
of the organs of fructification and to its application to systematic
botany. The imperfections, which are to be found even in this work,
are due to the circumstances of the time; in spite of Schmeidel’s and
Hedwig’s researches into the Mosses there was still the old obscurity
with regard to the organs of propagation in the Cryptogams, and this
rendered a right definition of the ideas, seed and fruit, extremely
difficult. But Gärtner made one great step in advance on this very
point when he showed that the spores of the Cryptogams were essentially
different from the seeds of Phanerogams, with which they had been
hitherto compared, because they contain no embryo; he called them
therefore not seeds, but gemmae. The second great hindrance to a true
conception of certain characters in fruits and seeds on the part of
Gärtner was the entire ignorance of the history of development which
then reigned; yet even here we see an advance, if only a small one,
made by him in his repeatedly going back to the young state for a more
correct idea of the organs.
Above all, Gärtner put an end to the blunder of regarding dry
indehiscent fruits as naked seeds, by rightly defining the pericarp
as in all cases the ripened wall of the ovary, and by considering its
strong or weak construction, its dry or pulpy condition, as a secondary
matter. It is obvious that the whole theory of the flower was thus
placed upon a better basis, since dry indehiscent fruits may come from
inferior or superior ovaries. But Gärtner’s theory of the seed is
one of his most valuable contributions to the science. After careful
consideration of the seed-envelopes, he submitted the inner portion
(nucleus) enclosed by them to a searching comparative examination;
he correctly distinguished the endosperm from the cotyledons, and
described the variations in its form and position. This was the more
needful, since Linnaeus had denied the existence of an ‘albumen’ in
plants, which Grew had already recognised and so named; to Linnaeus
it appeared to be of no use to the seed. Though Gärtner speaks of the
cotyledons as uniting with the embryo to form the nucleus of the seed,
yet his account shows that he regarded them as outgrowths of the embryo
itself. The uncertainty which still existed in the interpretation of
the parts of the seed is shown even in Gärtner by his curious notion of
a ‘vitellus,’ which in fact takes in everything that he was unable to
explain aright inside the seed; for instance, he makes the scutellum
in grasses, and even the cotyledonary bodies of Zamia a vitellus, and
applies the same name to the whole contents of the spores of Seaweeds,
Mosses, and Ferns. In spite of the striking defects connected with
this mistaken notion in his theory of the seed, his views far surpass
in clearness and consistency all that had hitherto been taught on the
subject. His giving the term embryo to that part of the seed which is
capable of development was also an advance in respect of logic and
morphology, in spite of his mistake in not admitting the cotyledons
which are attached to the embryo into the conception; this, however,
could easily be corrected at a later time. What Gärtner now named
the embryo, had been up to his time called the ‘corculum seminis,’
especially by Linnaeus and Jussieu; it was evidently thought that
Cesalpino’s phraseology was thus retained; but he, as we have seen,
understood by the words ‘cor seminis’ the spot where the cotyledons
spring from the germ, which spot he wrongly took for the meeting-point
of root and stem and the seat of the soul of the plant. And so at last
after two hundred years the word disappeared from use, which might
have reminded the botanist of Cesalpino’s views respecting the soul of
plants.
A work such as Gärtner’s could scarcely find a fruitful soil in
Germany, where some thirty years before even Koelreuter’s brilliant
investigations had met with little sympathy, and Conrad Sprengel’s
remarkable enquiries into the relations of the structure of the flower
to the insect-world in 1793 failed to be understood; Gärtner complains
in the second part, published in 1791, that not two hundred copies of
the first volume were sold in three years. But the work, which forms an
epoch in the history of botany, was better received in France, where
the Academy placed it as second in the list of the productions which
in later times had been most profitable to science; there lived the
man who was able to measure the whole value of such a work—Antoine
Laurent de Jussieu. But even in Germany, where plant-describing was
comfortably flourishing, there were not altogether wanting men who
knew how to estimate both the services of Gärtner and the importance
of the natural system. First among these was August Johann Georg Karl
Batsch, Professor in Jena from 1761 to 1802, who published in the
latter year a ‘Tabula affinitatum regni vegetabilis,’ with characters
of the groups and families. Kurt Sprengel, who was born in 1766, and
died as Professor of Botany in Halle in 1833, contributed still more
to the spread of clearer views respecting the real character of the
natural system and the task of scientific botany generally by numerous
works, and especially by his ‘Geschichte der Botanik,’ which appeared
in 1817 and 1818. But even this highly gifted and accomplished man
agreed with the Linnaean botanists in attributing an excessive value
to the describing of plants, as is shown in his history, where to exalt
the merits of the old botanists he gives figures of the plants first
described by them.
Meanwhile the meritorious efforts of these men were not in themselves
capable of directly advancing the natural system, or of greatly
increasing the number of its adherents in Germany, nor did it find
general acceptance in that country till it had made considerable
progress in the hands of the two foremost botanists of the time, De
Candolle and Robert Brown.
AUGUSTIN PYRAME DE CANDOLLE[37] (1778-1841) belongs to the number of
those distinguished investigators of nature, who at the end of the last
and the beginning of our own century made their native city Geneva a
brilliant centre of natural science. De Candolle was the contemporary
and fellow-countryman of Vaucher, Theodore de Saussure, and Senebier.
Physics and physiology especially were being successfully cultivated
at that time in Geneva, and Pyrame de Candolle was attracted to these
studies; among his youthful efforts are some important investigations
into the effect of light on vegetation, and the contributions which he
made to vegetable physiology in his great work on that subject will
be noticed in a later portion of this history. De Candolle turned his
attention to all parts of theoretical and applied botany, but his
importance for the history of the science lies chiefly in the direction
of morphology and systematic botany, and it is this which we will now
proceed to describe.
The amount and compass of De Candolle’s labours as a systematic and
descriptive botanist exceed those of any writer before or after him.
He wrote a series of comprehensive monographs of large families of
plants, and published a new edition of De Lamarck’s large ‘Flore
Française’ substantially altered and enlarged; and in addition to these
and many similar works and treatises on the geographical distribution
of plants, he set on foot the grandest work of descriptive botany that
is as yet in existence, the ‘Prodromus Systematis Naturalis,’ in which
all known plants were to be arranged according to his natural system
and described at length,—a work not yet fully completed, and in which
many other descriptive botanists of the last century participated, but
none to so large an extent as De Candolle, who alone completed more
than a hundred families. It is not possible to give an account in few
words of the service rendered to botany by such labours as these; they
form the real empirical basis of general botany, and the better and
more carefully this is laid, the greater the security obtained for the
foundations of the whole science.
But a still higher merit perhaps can be claimed for De Candolle,
inasmuch as he not only like Jussieu elaborated the system and its
fundamental principles in his descriptive works, but developed the
theory, the laws of natural classification, with a clearness and
depth such as no one before him had displayed. To this purpose he
applied morphological researches, which in profundity and wealth of
thought and in the fruitfulness of their results for the whole domain
of systematic botany far surpassed all that Linnaeus and Jussieu had
accomplished, and show us that while engaged in his splendid labours
in descriptive botany he had caught during his ten years’ residence
in Paris the true spirit of modern investigation of nature, as it had
been developed by the French naturalists of the end of the previous
century. Scarcely a trace is to be found in De Candolle of the
scholasticism of Cesalpino and Linnaeus, which occasionally makes its
appearance even in Jussieu. For instance, he dealt with morphology as
essentially the doctrine of the symmetry of form in plants, that is, he
found the basis of morphological examination in the relative position
and numbers of the organs, disregarding their physico-physiological
properties as of no account from the morphological point of view. He
was therefore the first who recognised the remarkable discordance
between the morphological characters of organs, which are of value
for systematic purposes, and their physiological adaptations to the
conditions of life, though it must at the same time be acknowledged,
that he did not consistently carry out this principle, but committed
grave offences against it in laying down his own system. It is a point
of the highest interest in De Candolle’s morphological speculations,
that he was the first who endeavoured to refer certain relations of
number and form to definite causes, and thus to distinguish what is
primary and important in the symmetry of plants from merely secondary
variations, as is seen in his doctrine of the abortion and adherence
of organs. In these distinctions De Candolle laid the foundation of
morphological views, which, though now modified to some extent, do
still contain the chief elements of morphology and the natural system;
but his morphological speculations were confined to the domain of
the Phanerogams, and chiefly advanced the theory of the flower; a
morphology of the Cryptogams was as little to be thought of in the
condition of microscopy before 1820, as the application of the history
of development to the establishment of morphological theories.
De Candolle published his morphology or doctrine of symmetry and his
theory of classification together in a book which appeared first
in 1813, with the title, ‘Théorie Élémentaire de la botanique ou
exposition des principes de la classification naturelle et de l’art de
décrire et d’étudier les végétaux,’ and again in 1819 in an improved
and enlarged edition. The second edition will be the one referred to in
the further account of his views. The second chapter of the second book
concerns us most at present. After alluding to the fact, that anatomy
and physiology are concerned with the structure of the individual
organ only so far as the power to fulfil its proper function depends
on the structure, he points out that the physiological point of view
is no longer sufficient when we are engaged in comparing the organs of
different plants. Though it is true that the function of the organs
is the most important for the life and permanence of the individual,
yet we find these functions modified in the case of homologous organs
in different plants; for the natural classification we must take into
consideration only the entire system of organisation, that is, the
symmetry of the organs. All organisms of a kingdom, he continues, have
the same functions with slight modifications; the immense amount of
variation in systematically different species depends therefore only
on the way in which the general symmetry of structure varies. This
symmetry of the parts, the discovery of which is the great object
in the investigation of nature, is nothing more than the sum total
(l’ensemble) of the positional relations of the parts. Whenever these
relations (disposition) are regulated according to the same plan,
the organisms exhibit a certain general resemblance to one another,
independently of the form of the organs in detail; when this general
resemblance is perceived, without any attempt to give any account of
it in the detail, we have what has been called habitual relationship;
but it is the task of the doctrine of symmetry to resolve this likeness
of habit into its elements, and to explain its causes. Without this
study of symmetry it may easily happen that two different kinds of
symmetry may be supposed to be alike, because they seem outwardly
alike to our senses, just as forms of crystals of different systems
may be confounded together for want of careful examination; the chief
thing is to know the plan of symmetry in every class of plants,
and the study of this is the foundation of every theory of natural
affinities. But success in this study depends on the certainty with
which organs are distinguished, and the distinguishing them must be
independent of changes of form, size, and function. He then shows that
the difficulties in the morphological comparison of organs, or, as we
should now say, in the establishing the homology, are due to three
causes; abortion, degeneration, and adherence (adhérence). These three
causes, by which the original symmetry of a class is changed and may
even be utterly obscured, are then fully illustrated by examples.
In respect to abortion he distinguishes that which is produced by
internal causes from that which is due to accidental and external ones;
he refers especially to the abortion of two loculaments in the fruit of
the horse-chestnut and the oak, to the suppression of the terminal bud
in some shrubs by the adjoining axillary buds, and to the fact that all
organs of plants may become abortive in a similar manner; for instance,
the sexual organs disappear entirely in the disk-flowers of Viburnum
Opulus, and one of the two sexes in the flower of Lychnis dioica. He
goes on to answer the question, how it is possible to discover the
symmetry in such cases; one method he finds supplied by monstrosities,
among which there are even some that may be regarded as a return to the
original symmetry, the cases known as peloria. Analogy or ‘induction’
is, he says, less certain, but of much more extensive application;
this is founded exclusively on the knowledge of the relative position
of organs. Armed with this, we find that the flower of Albuca, which
corresponds to a flower of Liliaceae in everything except in having
only three stamens, is to be considered one of the Liliaceae, because
it has three filaments placed between the three stamens exactly in
the position of the three other stamens in the Liliaceae; it must
be concluded therefore that they are abortive stamens. Similar
conclusions from analogy must be carried from species to species,
from organ to organ, and the great systematists have in fact done so.
In certain cases abortion is produced by defect, in others by excess
of nourishment, of which he gives examples. An important sentence
occurs in this place; everything in nature, he says, leads us to
believe that all organisms in their inner nature are regular, and that
different forms of abortion differently combined are the cause of all
irregularity; from this point of view the smallest irregularities
are important, because they lead us to expect greater ones in nearly
allied plants; and wherever in a given system of organisation there
are inequalities between organs of the same name, the inequality will
possibly reach a maximum, that is, end by annihilating the smallest
part. Thus in the Labiatae with two stamens, it is the two which in
other cases also are the smaller, which are here completely aborted.
When in Crassulaceae there are twice as many stamens as petals, those
that alternate with the petals are larger and earlier developed, and
we may therefore expect that those which are opposite the petals may
become abortive; and therefore we may place a genus like Sedum, in
which the latter are sometimes wanting, with Crassulaceae; but we could
not do so, if we found only the stamens that are superposed upon the
petals. It occurs sometimes, he continues, that an organ is prevented
from fulfilling its function by partial abortion. In this case it may
assume another function, as the abortive leaves of the vetch and the
abortive inflorescences of the vine are employed as tendrils. In other
cases the abortive organ appears to be quite useless, as for instance
many rudimentary leaves. All such useless organs, says De Candolle,
exist only in consequence of the primitive symmetry of all organs.
Finally the abortion may be so complete that no trace of the organ
remains, of which case there are however two kinds, one where the organ
is at first perceptible and afterwards quite disappears, as in the
abortive loculaments in the fruit of the oak; in other instances no
trace is to be seen from the first of the abortive organs, as happens
with the fifth stamen of Antirrhinum.
All that has here been said might be alleged word for word in proof
of the theory of descent, but our author is an adherent of the dogma
of the constancy of species; what from his point of view he really
means by abortion is difficult to say, for the object which is aborted
is wanting. If species are constant, and therefore of absolutely
distinct origin, we must not speak of abortion; we can only say
that an organ which is present or large in one species is small or
wanting in another. In introducing the idea of abortion De Candolle
at once goes beyond the dogma of the constancy of species, without
being clear in his own mind with regard to this important step.
His proceeding shows that facts lead even a defender of constancy
against his will to theories which run counter to that dogma. This
is confirmed by his perception of the correlation of growth, which
is connected with abortion; he points to the fact that owing to the
disappearance of sexual organs in the disk-flowers of Viburnum Opulus
the corollas become larger, as do the bracts of the abortive flowers
of Salvia Horminum; similarly he regards the disappearance of the
seeds in Ananas, Banana, and the Bread-fruit tree as the cause of the
enlargement of the pericarps; it does not escape him, that the fertile
flower-stalks in Rhus Cotinus remain naked, while an elegant pubescence
forms on the barren ones; the leaf-like expansion of the leaf-stalks
of Acacia heterophylla, which do not develop their laminae, he refers
also to this correlation of growth. He finds the most remarkable
example of the kind in the doubling of flowers, where according to his
view the disappearance of the anthers is a condition of the corolline
expansion of the filaments; in the same way sometimes the carpel is
changed into a petal through the disappearance of the stigma. Though in
many of these cases it is quite possible to conceive of the relations
of cause and effect in the reverse way, yet De Candolle’s principle of
correlation will be equally applicable.
The second cause by which the symmetry may be obliterated, namely
degeneration, asserts itself in the formation of thorns, of threadlike
prolongations of membranous expansions, and in the production of fleshy
parts, or of parts with dry membranes.
The third kind of departure from the symmetrical plan is the adherence
of parts, the theory of which he grounds first and chiefly on the
phenomena of grafting, and then passes to more difficult cases. The
close packing of the ovaries in some species of honeysuckle, is, he
says, the primary cause of their adherence. This therefore does not
depend on the plan of symmetry, but upon an accident, which however is
constant in its appearance, owing to the specific constitution of such
plants. In connection with the phenomena of adherence he next considers
the question whether a structure composed of several parts, as for
instance a compound ovary, should be considered as originally simple
and afterwards divided into parts, or whether the converse is the true
account, and he says that we must examine each particular case and
decide which is the correct conception. Thus it may be shown that the
perfoliate leaves of honeysuckles, as well as the involucres of many
Umbelliferae, and monosepalous calyces and monopetalous corollas are
due to adherence, and he proceeds to prove that ovaries with several
loculaments and several parts have in like manner been formed by
adherence of two or more carpellary leaves, and concludes by pointing
out the systematic importance of such considerations. Further on he
takes occasion to speak of the significance of the relative number
of the parts of the flower, on which head he says much that is good,
but does not thoroughly investigate the matter; it was not till a
later time that Schimper’s doctrine of phyllotaxis made it possible to
express these relations of number and position more precisely.
He concludes his rules for the application of his morphology to the
determination of relations of affinity with the declaration, that the
whole art of natural classification consists in discerning the plan
of symmetry, and in making abstraction of all the deviations from it
which he has described,—much in the same way as the mineralogist seeks
to discover the fundamental forms of crystals from the many derivative
forms. It is obvious that all this teaching was a great step in advance
upon the right path, that De Candolle has here given utterance for
the first time to an important principle of morphology and systematic
botany; nevertheless he did not succeed in always consistently carrying
out his own principle; he was true to himself only in the determination
of small groups of relationship; in framing the largest divisions of
the vegetable kingdom he entirely lost sight of the rule which he had
himself laid down, that the morphological character of organs and the
extent to which it can be turned to account for systematic purposes is
entirely independent of their physiological character, and that the
most important physiological characters are just those which are of
quite subordinate importance in the determination of affinities. In
spite of this strange inconsistency, to De Candolle belongs the merit
of being the first to point emphatically to the distinction between
morphological and physiological marks, and to bring clearly to light
the discordance between morphological affinity and physiological habit;
but in this discordance lurks a problem, which could only be solved
forty years later by Darwin’s theory of selection. A genuine inductive
process alone could reveal these remarkable relations between the
morphological and physiological characters of organs. But it is at the
same time true that De Candolle could not have made this discovery,
if his predecessors had not already established a large number of
affinities. It was while he was engaged in an exact comparison of forms
already recognised as undoubtedly related to one another, that that
which he called the plan of symmetry, and which was afterwards named
a type, revealed itself to him; and as he examined it more closely,
and compared it with peculiarities of habit in different plants formed
on the same plan, he discovered certain causes, by means of which the
deviations were to be explained; these were abortion, degeneration,
and adherence. By attending to these he succeeded in discovering
affinities that had been hitherto doubtful or unknown; this was at all
events the true inductive way of advancing the system, and whatever
the earlier systematists had effected that was really valuable had
been effected virtually in the same way, only they never arrived at a
clear understanding of their own mode of proceeding; they had followed
unconsciously the method which De Candolle clearly understood and
consciously pursued.
The majority of De Candolle’s successors were far from fully
appreciating the entire significance of his theory, its importance as
a matter of method and principle; on the contrary in the search for
affinities they continued to surrender themselves to a blind feeling
rather than to a clearly recognised method, and the same must be
said unhappily of De Candolle himself, when he was dealing with the
establishment of the large divisions of the vegetable kingdom. With
equal surprise we find him in the book before us, in which he has
developed the true method in systematic botany, expressing the opinion
that the most important physiological characters must be employed for
the primary divisions of the system, and this idea is not improved
by the fact that he ascribes to the organs physiological characters
which they do not really possess; thus he regards the vessels as the
most important organs of nutrition, which they are not in fact, and
upon this double error he builds his primary division of the whole
vegetable kingdom into vascular and cellular plants, and then by a
third mistake believes that this division coincides with the division
of plants into those which have and those which have not cotyledons.
The already established division into Monocotyledons and Dicotyledons,
which rests upon a leading and purely morphological mark, is spoilt
by De Candolle through his following Desfontaines in ascribing to
the Dicotyledons a different mode of growth in thickness from that
of the Monocotyledons, and characterising the one as exogenous, the
other as endogenous. But this notion is utterly incorrect, as von Mohl
showed twelve years later; and if it were correct, it would still be
unimportant in a systematic point of view, because it appeals to a mark
which is morphologically of quite subordinate importance. The worst
consequence of these mistakes was, that the Vascular Cryptogams were
introduced into the same class with the Monocotyledons,—a decided step
backwards, if we compare De Candolle’s system with that of Jussieu.
In spite of these grave defects in the primary divisions of the whole
vegetable kingdom De Candolle’s system deserved the fame which it
acquired and long maintained; it had this advantage over Jussieu’s
system that in the class of Dicotyledons, the largest division of the
whole kingdom, larger subdivisions appeared, and these served to unite
families that were in many points essentially related; the Dicotyledons
were in fact divided first of all into two artificial groups according
to the presence of two floral envelopes or one; the first and much
the larger of these was again broken up into a series of subordinate
groups, which pointed in many ways to natural affinities. That these
groups, which have only quite recently been materially altered, did to
a very considerable extent take account of natural affinities, is due
to the fact that De Candolle in framing them really followed his own
rules, whereas the superior divisions, which are artificial, owe their
existence to his disregard of them.
De Candolle declared emphatically against the old notion, that the
vegetable system answers to a linear series,—a notion which sprang
from a misunderstanding of the saying, ‘Natura non facit saltus,’—and
demonstrated its impossibility by examples; but he allowed himself
to be too much influenced by the idea which had been thrown out by
Linnaeus, and taken up by Giseke, Batsch, Bernardin de St. Pierre,
L’Heritier, Du Petit-Thouars and others, that the vegetable kingdom
might be compared as respects its grouping to a geographical map, in
which the quarters of the globe answer to the classes, the kingdoms
to the families, and so on. If the theory of descent is to a certain
degree compatible with the idea of a linear sequence from the most
imperfect to the highest forms of plants, it is quite incompatible
with the above comparison; and systematic investigation, led astray
from the right path, is in danger of ascribing the importance of
real affinities to mere resemblances of habit, incidental analogies,
by which a group of plants appears to be connected with five or six
others. In exhibiting his system on paper De Candolle allowed the use
of the linear sequence as a convenience, for here it was not, he said,
a matter of any importance, since the true task of the science is to
study the relations of symmetry in each family and the mutual relations
of families to one another; yet in a linear presentation of the system
for didactic purposes the sequence ought not to begin with the most
simple plants, for these are the least known, but with the most highly
developed. Thus De Candolle was the means of removing from the system
the last trace of anything which harmonised with an ascending and
uninterrupted development of forms. Resting on the doctrine of the
constancy of species, and assuming that every group of relationship is
founded on a plan of symmetry round which individual forms are grouped
as crystals round their parent form, De Candolle was quite consistent
in his views. The mode of representation came to prevail in the
vegetable kingdom which De Candolle’s contemporary, Cuvier, an equally
sturdy defender of the dogma of constancy, had introduced in the animal
kingdom as the type-theory. Thus the most splendid results obtained by
induction were united in the case of De Candolle with the barren dogma
of the constancy of species, which, as Lange wittily remarks, comes
direct from Noah’s ark, to form an intimate mixture of truth and error;
nor did De Candolle’s many adherents succeed in unravelling the coil,
though they removed the chief errors from his system and introduced
many improvements.
To these remarks may be appended a table of the main divisions of De
Candolle’s system of 1819, which so far as it is presented in linear
arrangement he calls expressly an artificial system.
I. Vascular plants or plants with cotyledons.
1. Exogens or Dicotyledons.
A. With calyx and corolla:
Thalamiflorals (polypetalous hypogynous),
Calyciflorals (polypetalous perigynous),
Corolliflorals (gamopetalous).
B. Monochlamydeous plants (with a single floral envelope).
2. Endogens or Monocotyledons.
A. Phanerogams (true Monocotyledons),
B. Cryptogams (vascular Cryptogams including Naiadeae).
II. Cellular plants or Acotyledons.
A. With leaves (Muscineae),
B. Without leaves (Thallophytes).
The number of families, with Linnaeus 67, with A. L. de Jussieu 100,
was increased by De Candolle to 161.
If the principles of comparative morphology laid down by De Candolle
were at first prevented from being rapidly disseminated in Germany by
the philosophical tendencies then reigning among its botanists, and
especially by the obscurities of Goethe’s doctrine of metamorphosis,
yet these principles and his views also on the natural system won
their way by degrees to acknowledgment and acceptance; and after the
year 1830 the study of the system was prosecuted by the botanists of
Germany, as well as by those of England and France, as the proper
object of the science. We may even say that the impulse given by De
Candolle worked more powerfully from that time forward in Germany
than in France. It may be said too of De Candolle’s contemporary, the
Englishman ROBERT BROWN[38] (1773-1858), whose chief labours fall
in the period between 1820 and 1840, that he, like De Candolle, was
better appreciated during that time in Germany than in any other
country. Robert Brown, who spent the five years from 1801 to 1805
in Australia, studied the flora of that quarter of the world, and
discussed in numerous essays the botanical results of various journeys
made by other naturalists in polar regions and in the tropics. In this
way he found opportunity to leaven the ideas, which through Humboldt’s
influence had become predominant respecting the geography of plants,
with the spirit of the natural system; he also made the morphology and
systematic position of a number of families the subject of critical
investigation.
Robert Brown’s literary efforts were limited to these monographs; he
nowhere attempted to give a connected account of the principles which
he follows in them, an exposition of his morphology or a theory of
classification, nor did he frame a new system. The results of his
studies which were really fruitful and served to advance the science
are to be found in the more general remarks, which he managed to insert
quite incidentally in his monographs. In this way he succeeded in
clearing up the morphology of the flower and with it the systematic
position of some difficult families of plants, such as the Grasses,
Orchids, Asclepiads, the newly-discovered Rafflesiaceae and others, and
to throw new light at the same time on wider portions of the system;
in his considerations on the structure and affinities of the most
remarkable plants, which had been collected in Africa by different
travellers in the years immediately following 1820, he discussed
difficult and remarkable morphological relations in the structure
of the flower. He referred especially in this essay (1826) to the
relations between the numbers of the stamens and carpels, and those of
the floral envelopes in the Monocotyledons and Dicotyledons, and showed
how these typical, or as he calls them in De Candolle’s phraseology,
symmetrical relations were changed by abortion, while he entered at
the same time into a more exact determination of the position of the
aborted and of the perfect organs, in order to discover new relations
of affinity. His most valuable work in this direction is a paper on
a genus Kingia, discovered in New Holland in 1825; the structure of
the seeds in this genus led him to seek more accurate knowledge of the
unfertilised ovule in the Phanerogams generally, and especially in
the Cycads and Conifers. In spite of the labours of Gärtner and the
later researches of Treviranus, there was still considerable obscurity
attaching to the theory of the seed, for no one had yet succeeded in
referring the position of the embryo in the ripe seed to a general law.
For this it was necessary to submit the ovule before fertilisation
to careful examination, and Robert Brown carried out this first step
to a history of development with great success; he was the first to
distinguish the integuments and the nucleus in the ovule, and the
embryo-sac in the nucleus, parts which Malpighi and Grew had indeed
observed but had not brought out with perfect clearness. The micropyle
and the hilum of the seed had not yet been properly distinguished, but
had been to some extent even confounded with one another. Robert Brown
showed that the hilum answers to the point of attachment of the ovule,
while the micropyle is a canal formed by the integuments of the ovule
and leading to the summit of the nucleus; that in anatropous ovules
the micropyle lies beside the hilum, in orthotropous ovules opposite
to it; that the embryo in the embryo-sac (amnion) is always formed at
the spot which lies nearest the micropyle, and that the radicle of the
embryo is always turned towards the micropyle,—facts which at once
established the general rule by which to determine the position of the
embryo in the seed and in the fruit. He also gave the first correct
explanation of the endosperm as a nourishing substance formed inside
the embryo-sac after fertilisation, and more than this, he was the
first to distinguish the perisperm as a substance formed outside the
embryo-sac in the tissue of the nucleus.
In this way Robert Brown established morphological relations in the
organisation of the seed of the Monocotyledons and Dicotyledons, which
count among the most important principles of classification in these
classes; he was still more happy in being the first to detect the
peculiar structure of the flower of Conifers and Cycads, as compared
with that of other flowering plants; it was he who perceived that
what had been hitherto called a female flower in these plants was
really a naked ovule, a view which Trew of Nüremberg had, it is true,
suggested in the year 1767. He also called attention to the agreement
in structure of the male and female organs in these families. Thus
one of the most remarkable facts in vegetation, the gymnospermy of
the Conifers and Cycads, was for the first time established, and this
led afterwards through Hofmeister’s investigations to the important
result, that the Gymnosperms, which had been up to that time classed
with Dicotyledons, are to be regarded as co-ordinate with Dicotyledons
and Monocotyledons, forming a third class through which remarkable
homologies were brought to light in the propagation of the higher
Cryptogams and the formation of seeds in Phanerogams. No more important
discovery was ever made in the domain of comparative morphology and
systematic botany. The first steps towards this result, which was
clearly brought out by Hofmeister twenty-five years later, were secured
by Robert Brown’s researches, and he was incidentally led to these
researches by some difficulties in the construction of the seed of an
Australian genus. He discussed in a similar manner, if not always with
such important results, a great variety of questions in morphology
and systematic botany; even purely physiological problems were raised
by him in this peculiar way, and especially the question how the
fertilising matter of the pollen-grains is conveyed to the ovule;
he had already concluded from the position of the embryo that it is
conveyed through the micropyle and not through the raphe and the hilum,
as was then supposed, and he was the first also to follow the passage
of the pollen-tubes in the ovary of Orchids up to the ovules; but this
is a point which will be more properly considered in the history of the
sexual theory.
The peculiar character of the natural system as compared with every
artificial arrangement is brought out into higher relief by Robert
Brown than by Jussieu and De Candolle, and he succeeded better
than any of his predecessors in separating purely morphological
and systematically valuable relations of organisation from the
physiological adaptations of organs. While the majority of systematists
surrendered themselves to the guidance of a blind feeling in the
discovery of affinities, their correct determinations being the
accidental result of instinct and unconscious operations of the
understanding, Brown endeavoured to give an account to himself in every
case of the reasons why he took this or that view of the relationships
which he determined; from what was already established and indubitable
he gathered the value of certain marks, in order to obtain rules for
the determination of unknown relationships. In this way he discovered
also, that marks, which are of great value for classification within
the limits of certain groups of affinity, may possibly prove to be
valueless in other divisions. Thus Robert Brown in his numerous
monographs supplied the model, by which others might be guided in
further applying and completing the method of the natural system; and
in this respect he was met by the botanists of Germany in the spirit
of the best good-will and most profound appreciation, as is shown
by the fact that a collection of his botanical works, translated by
different German botanists, was edited in five volumes by Nees von
Esenbeck as early as the period between 1825 and 1834. The natural
system established itself in Germany through the labours of Brown and
De Candolle; and the more correct appreciation of it as compared with
the sexual system of Linnaeus was promoted by a work of Carl Fuhlrott
which appeared in 1829, in which the systems of Jussieu and De Candolle
are compared with those of Agardh, Batsch, and Linnaeus, and the
superiority of the natural system is clearly set forth. A still greater
effect in this direction was produced by the appearance in 1830 of the
‘Ordines naturales plantarum’ of Bartling, an independent contribution
to this department of botany, and a distinct advance upon what had
hitherto been effected. The contemporary monographs of Roeper on the
Euphorbiaceae and Balsamineae and his treatise ‘De organis plantarum’
(1828), are an able, independent, and logical application of the
principles of the morphology of the flower laid down by De Candolle and
Brown to the elucidation of morphological and systematic conceptions.
But the new methods of investigation introduced by De Candolle and
Robert Brown had to encounter in Germany, and to some extent in France
also, not only the antiquated views of Linnaeus, but, what was still
worse, the erroneous notions of the nature-philosophy founded by
Schelling. The misty tenets of this philosophy could scarcely find
a more fruitful soil than the natural system with its mysterious
affinities, and Goethe’s doctrine of metamorphosis contributed not
a little to increase the confusion. These historical phenomena will
be further considered in the following chapter; at present we are
more concerned to show how the professed systematists pursued the
path opened by De Candolle and Brown. And here it must be noticed
that from about the year 1830, in Germany especially, morphological
enquiry became separated as a special subject from systematic botany;
it became more and more the fashion to treat the latter as independent
of morphology, and thus to forsake the source of deeper insight which
comparative and genetic morphology alone can open to the systematist;
morphology on the other hand took a new flight, and as it thus
developed itself apart from pure systematic botany, its progress must
be described by itself in a later portion of this history.
If advance in systematic botany depended on the number of systems that
were proposed from 1825 to 1845, that period must be looked upon as
its golden age; no less than twenty-four systems made their appearance
during these twenty years, without counting those which were inspired
by the views of the nature-philosophy. There was great and spreading
growth, but no corresponding depth; no really new points of view were
opened for classification, and as regards the true principles of the
natural system there were symptoms of evident decline rather than of
advance, as will be shown below. Improvements were effected certainly
in the details of the system, since botanists generally adhered to
the principles laid down by De Candolle, Jussieu, and Brown. Families
were cleared up and better defined, and groups of families were
proposed which assumed more and more the appearance of natural cycles
of relationship. The class more especially treated was the extensive
one of the Dicotyledons, in which the families, continually growing
more and more numerous, were in Jussieu’s arrangement a chaos, but had
been united into larger groups in a somewhat artificial manner by De
Candolle. Here we see once more how the formation of the system rises
step by step from the particular to the more general; at an earlier
period genera were constructed out of species, and families out of
genera, and during the years from 1820 to 1845 the families were united
into more comprehensive groups; but these orders or classes were not
yet grouped together in such a manner as to ensure the separation of
the largest divisions of the vegetable kingdom in a natural manner.
The great class of Dicotyledons is not even yet so arranged that the
smaller aggregates of families connect satisfactorily one with another.
Nevertheless a considerable advance was made by the establishment of a
large number of smaller groups of families, and Bartling and Endlicher
were especially successful in founding such groups and supplying them
with names and characters.
If on the other hand we turn to the primary divisions of the vegetable
kingdom, we find that certain large and natural groups came to be most
generally recognised and placed in the front rank in every scheme; such
were the groups of the Thallophytes, Muscineae, Vascular Cryptogams,
Gymnosperms, Dicotyledons and Monocotyledons. But the coordination
of these great divisions of the whole vegetable kingdom was far from
being rightly understood. It was usage rather than anything else, which
gradually put them forward as primary types; in the systems themselves
some received too great, others too little prominence, or other groups
of doubtful character were admitted alongside of them. Bartling, for
instance, whose system up to 1850 or even longer may rank as one of
the most natural, adheres to De Candolle’s division of the vegetable
kingdom into cellular and vascular plants, and rightly divides the
former into two main groups, Thallophytes and Muscineae (Homonemeae and
Heteronemeae), while he separates the latter into Vascular Cryptogams
and Phanerogams; but the Phanerogams are divided into Monocotyledons
and Dicotyledons, which again are distributed into four groups, one
of these being characterised by the presence of a vitellus, that is,
of an endosperm surrounded by a perisperm,—a thoroughly artificial
division. The three other divisions are named apetalous, monopetalous,
and polypetalous, but the Coniferae and Cycadeae are placed in
the apetalous division. Less satisfactory is the primary division
into Thallophytes and Cormophytes proposed by ENDLICHER[39], the
latter separating into the divisions Acrobrya (Muscineae, Vascular
Cryptogams, and Cycads), Amphibrya (Monocotyledons), and Acramphibrya
(Dicotyledons and Conifers); the names of the three latter groups,
the first of which is utterly unnatural, are founded on erroneous
assumptions respecting growth in length and thickness, which Endlicher
borrowed from Unger. While Endlicher’s great work has continued down
to our own time to be indispensable to the botanist as a book of
reference on account of the fulness of its descriptions of families
and genera, the system projected by Brongniart in 1843 has acquired a
sort of official authority in France. The whole vegetable kingdom is
here distributed into two divisions, Cryptogams and Phanerogams, and
the former are incorrectly characterised as asexual, the latter as
having distinction of sex. The Phanerogams, divided into Monocotyledons
and Dicotyledons, are distributed into groups in a manner that is
not satisfactory; but the system has one merit, that it keeps the
Gymnosperms together in one body; and if they are incorrectly classed
with the Dicotyledons, it was still a sign of progress, that Robert
Brown’s discovery of gymnospermy was to some extent practically
recognised. The system devised by JOHN LINDLEY[40] attained to about
the same importance in England as attached to those of Bartling
and Endlicher in Germany, and that of Brongniart in France. After
various earlier attempts he proposed a system in 1845, in which, as
in Brongniart’s arrangement, the Cryptogams are characterised as
asexual or flowerless plants, the Phanerogams as sexual or flowering
plants; the former are divided into Thallogens and Acrogens, the
Phanerogams into five classes; (1) Rhizogens (Rafflesiaceae, Cytineae,
Balanophorae); (2) Endogens (parallel-nerved Monocotyledons); (3)
Dictyogens (net-veined Monocotyledons); (4) Gymnogens (Gymnosperms);
(5) Exogens (Dicotyledons). This classification is one of the most
unfortunate that were ever attempted; the systematic value of the
Rhizogens is much overrated on account of their striking habit; the
Monocotyledons are separated into two classes on the strength of an
unimportant mark. The characters assigned to all these groups are on
the whole thoroughly faulty.
These systems have been selected for notice from among many others,
because they attained an extended notoriety and importance from the
circumstance that their authors, Brongniart excepted, made them the
occasions of comprehensive descriptions of the whole vegetable kingdom,
and again because it would be superfluous for our present purpose to
bestow a closer consideration on the systems of less eminent men.
Whoever desires further information on the matter will find it in the
introduction to Lindley’s ‘Vegetable Kingdom’ of 1853.
If we consider the principles and points of view adopted in these
systems, one thing especially strikes us, that, except in the case
of Bartling, physiologico-anatomical marks were employed along with
morphological ones to characterise the primary divisions; their authors
fell into the mistake committed by De Candolle, and unfortunately
these very marks rested in part or wholly on misapprehensions, as in
Endlicher’s division into Acrobrya, etc., and Lindley’s classes of
Rhizogens and Dictyogens. It was still more unfortunate that individual
systematists obstinately refused to accept well authenticated facts,
which it is true had not been discovered by systematists, but were
nevertheless of the highest value for the system. It is scarcely
credible that Lindley in 1845, and again in 1853, maintained the
distinction between endogenous and exogenous growth in stems, though
Hugo von Mohl had in 1831 produced decisive proof that this distinction
laid down by Desfontaines and adopted by De Candolle had no real
existence. The same was the case with the characters of the Cryptogams,
in which the mark of having no sexual organs was repeatedly adopted
as running through the whole class, although various instances of
sexuality in Cryptogams were known before 1845; Schmidel had described
the sexual organs of the Liverworts about the middle of the previous
century, Hedwig those of the Mosses in 1782, and Vaucher in 1803 had
suggested that the conjugation of Spirogyra among the Algae should be
regarded as a sexual act; the systematists in fact did not know what to
make of these intimations.
It was again a misfortune that the systematists in their labours
often neglected to distinguish between the search for marks and the
use to be made of them; the examination of all possible marks should
lead to the establishing the systematic importance of certain fixed
marks or their value for classification. When research has done its
work, then it is sufficient in exhibiting the system to put forward
only the prominent marks; and frequently a single one suffices to
unite a natural group. Such a leading mark is like the standard of a
regiment; its significance is not great in itself, but it serves the
great practical purpose of indicating a whole group of marks which are
connected with it. It was a still greater misfortune that scarcely any
systematist after De Candolle endeavoured to form a clear conception
in his own mind of the principles on which the natural system must be
elaborated, and to set them forth in a connected form as the theory
of the system. The student had to accept the arrangement offered
him as a fact simply without understanding it, and the systematists
themselves usually followed only a blind feeling in the framing of
their groups, and never unfolded the grounds of their proceeding
with logical distinctness. In this respect John Lindley forms an
honourable exception, inasmuch as he did, on several occasions after
1830, give full expositions of his views on the principles of natural
classification, and like De Candolle endeavoured to develop a theory
of the system[41]. But he deserves credit only for the endeavour,
for the principles themselves which he laid down are not only to a
great extent incorrect, but they are opposed to his own and to every
other natural system. We find this opposition between theory and
practice much more strongly marked in Lindley than in De Candolle; the
cases only are so far different, that De Candolle laid down correct
principles for the determination of affinities, but in some cases
did not follow them, whereas Lindley deduced quite incorrect rules
of system from existing and long-established natural affinities. The
consideration of all the systems framed up to the year 1853 shows
clearly that the characters of truly natural groups are to be found
only in morphological marks; yet Lindley enunciates the principle that
a mark, or, as he incorrectly says, an organ, is more important for
classification in proportion as it possesses a higher physiological
value for the preservation and propagation of the individual. If this
were true, nothing would be easier than to frame a natural system of
plants; it would suffice to divide plants first of all into those
without and those with chlorophyll, for the presence of chlorophyll
is more essential than that of any other substance to the nourishment
of plants, and its physiological importance is therefore pre-eminent;
in that case of course such Orchideae as have no chlorophyll, the
Orobancheae, Cuscuta, Rafflesia, etc., would form one class with the
Fungi, and all other plants the other. It is very important for the
existence of a plant whether its organisation is adapted to its growing
in water, or on dry land, or underground, and if we took Lindley
at his word, he would be obliged to bring the Algae, Rhizocarps,
Vallisnerias, water Ranunculuses, Lemna, etc., into one group. It is
very important for the existence of a plant whether it grows upright
of itself, or climbs upwards by the aid of tendrils or of a twining
stem or otherwise, and accordingly we might on Lindley’s principle
collect certain ferns, the vine, the passion-flower, many of the pea
kind, etc., into one order. It is obvious that Lindley’s main axiom
of systematic botany appears in this way utterly unreasonable; yet
by this principle he judges of the systematic value of anatomical
characters, those of the embryo and endosperm, of the corolla and the
stamens, everywhere laying stress on their physiological importance,
which in these parts has really little systematic value. This mode of
proceeding on the part of Lindley, compared with his own system, which
with all its grave faults is still always a morphologically natural
system, proves that like many other systematists, he did not literally
and habitually follow the rules he himself laid down, for if he had,
something very different from a natural system must have been the
result. The success which was really obtained in the determination of
affinities was due chiefly to a correctness of feeling, formed and
continually being perfected by constant consideration of the forms of
plants. It was still therefore virtually the same association of ideas
as in de l’Obel and Bauhin, operating to a great extent unconsciously,
by which natural affinities were by degrees brought to light; and men
like Lindley, of pre-eminent importance as systematists, were, as the
above examples show, never clear about the very rules by which they
worked. And yet in this way the natural system was greatly advanced in
the space of fifty years. The number of affinities actually recognised
increased with wonderful rapidity, as appears from a comparison of the
systems of Bartling, Endlicher, Brongniart, and Lindley, with those
of De Candolle and Jussieu. Nothing shows the value of the systems
thus produced before 1850 as classifications of the vegetable kingdom
more forcibly than the fact that a clear and methodical thinker like
Darwin was able to draw from them the chief supports of the theory
of descent. For it is quite certain that Darwin has not framed his
theory in opposition to morphology and system, and drawn it from any
hitherto unknown principles; on the contrary, he has deduced his most
important and most incontestable propositions directly from the facts
of morphology and of the natural system, as it had been developed up to
his time. He is always pointing expressly to the fact that the natural
system in the form in which it has come to him, which he accepts in the
main as the true one, is not built upon the physiological, but upon
the morphological value of organs; it may, he says, be laid down as a
rule, that the less any portion of the organisation is bound up with
special habits of life, the more important it is for classification.
Like Robert Brown and De Candolle, he insists upon the high importance
for purposes of classification of aborted and physiologically useless
organs; he points to cases in which very distant affinities are brought
to light by numerous transition-forms or intermediate stages, of which
the class of the Crustaceae offers a specially striking example in
the animal kingdom, while certain series of forms of Thallophytes,
the Muscineae, the Aroideae and others, may be adduced as instances
of the same kind in the vegetable world; in such cases the most
distant members of a series of affinities have sometimes no one common
mark, which they do not share with all other plants of a much larger
division. From these and other similar statements of Darwin we see
plainly, that he actually did gather from existing natural systems
of plants and animals the rules by which systematists had worked,
but which they themselves observed only more or less unconsciously,
and never with a full and clear recognition of them. He says quite
rightly, when the investigators of nature are practically engaged with
their task, they do not trouble themselves about the physiological
value of the characters which they employ for the limiting a group
or the establishment of a single species. Darwin clearly perceived
and consistently kept in view the discordance between the systematic
affinity of organisms and their adaptation to the conditions of life,
which De Candolle had already but imperfectly recognised. The clear
perception of this discordance was in fact the one thing needed to
mark the true character of the natural system, and to make the theory
of descent appear as the only possible explanation of it. The fact
which morphologists and systematists had painfully brought to light,
but had not sufficiently recognised in its full importance, that
two entirely different principles are united in the nature of every
individual organism, that on the one hand the number, the arrangement,
and the history of the development of the organs of a species point to
corresponding relations in many other species, while on the other hand
the manner of life and the consequent adaptation of the same organs
may be quite different in these allied species. This fact admits of no
explanation but the one given by the theory of descent; it is therefore
the historical cause and the strongest logical support of that theory,
and the theory itself is directly deduced from the results which the
efforts of the systematists have established. That the majority of
systematists did at first distinctly declare against the theory of
descent can surprise no one who observes that they were so little able
to give an account of their own mode of procedure, as appears in so
striking a manner from Lindley’s theoretical speculations.
One consequence of this want of clearness in combination with the
dogma of the constancy of species has been already mentioned in the
introduction; namely, the notion professedly adopted by Lindley,
Elias Fries, and others, that an idea lies at the foundation of every
group of affinities, that the natural system is a representation of
the plan of creation. But the question, how such a plan of creation
could explain the strange fact that the physiological adaptations
of organs to the conditions of life have nothing at all to do with
their systematic connection, was quietly disregarded; and in fact the
notion, founded on Platonic and Aristotelian philosophy, of a plan
of creation and of ideal forms underlying systematic groups, could
not explain this discordance between morphological and physiological
characters. It would be easy to maintain the view of the systematists,
that the natural system represents a plan of creation, if physiological
and morphological characters went always truly hand in hand, if the
adaptation of the organs to the conditions of life in the species were
perfect; but facts show that the adaptation is in the best of cases
comparatively imperfect, and that it is in all cases brought about by
the accommodation to new requirements of organs which originally served
to other functions.