I. HORTICULTURAL AND BOTANICAL FRUITS
MATERIAL.—Green ears of corn or wheat, fresh pods of beans, young
fruits of apple, grape, tomato, melon, buckeye, chestnut, or pecan.
A young fruiting stem of squash, gourd, or tomato.
APPLIANCES.—Coloring fluid, glasses of water, a piece of cardboard,
tin-foil, vaseline.
EXPERIMENT 87. WHERE DO THE FOOD SUBSTANCES CONTAINED IN FRUITS
COME FROM?—Apply your food tests to the pulp of a young apple,
squash, bean pod, chestnut, buckeye, or a “green” ear of corn or
wheat, and see what it contains. Test the stem and roots of a plant
of the same kind in the same way. Do you find the same foods in
them? Where is the food stored?
EXPERIMENT 88. THROUGH WHAT PARTS OF THE STEM AND FRUIT DO WATER
AND NOURISHMENT TRAVEL TO THE SEED?—Cut a young squash or cucumber
from the vine, leaving stem enough to insert by its cut end in a
glass of eosin solution. Leave for two or three days, then make a
vertical section through the stem and fruit. What course has the
liquid followed? Can you trace some of it into each seed? Do you
see now a use for the seed stalk and the rhaphe?
EXPERIMENT 89. DOES THE SURFACE OF FRUITS GIVE OFF WATER BY
TRANSPIRATION?—Try Exp. 59, using in place of leaves a young
squash, eggplant, or a bunch of grapes, and after a day or two
notice whether any moisture has been given off. If the fruit skin
gives off moisture, it is natural to expect that it would be
provided with stomata, like other transpiring organs. To find out
whether this is so, place a thin piece of the outer epidermis of
a grape, tomato, plum, or apple under the microscope. Do you find
stomata on any of them? Do you see anything else? Try the skin of
an apple, and compare the corky dots you find there with those on
the bark of a young dicotyl stem (118) and decide what they are.
EXPERIMENT 90. WILL FRUITS RIPEN WELL IN THE ABSENCE OF LIGHT AND
AIR?—Envelop a number of immature fruits in bags of dark cloth or
paper so that no light can reach them. Keep a number of others well
coated with oil or vaseline, and watch. Do the fruits so treated
mature as quickly or develop as fully as those of the same kind
left untreated?
[Illustration: PLATE 12.—The improvement of fruits by cultivation and
selection: 1, the common wild gooseberry; 2, Houghton gooseberry,
seedling of the wild form; 3, Downing gooseberry, seedling of the
Houghton. (All natural size, adapted from Bailey.)]
EXPERIMENT 91. WHAT IS THE USE OF THE RIND TO THE FRUIT?—Select
two apples of equal size, peel one, and weigh both. After 12 to 24
hours, weigh them again. Which shows the greater loss in weight?
Leave peeled and unpeeled fruits in an exposed place and see which
is the more readily attacked by insects. Which decays the sooner?
What are some of the uses of the rind?
=282. What is a fruit?=—Horticulturally and commercially the
distinction between a fruit and a vegetable depends very much upon
the use we make of it—whether as food, or as a mere gratification of
the palate. Broadly speaking, those fruits that are lacking in sugar,
as the tomato and cucumber, are classed as vegetables. Botanically, a
fruit is any ripened seed vessel, or ovary, with such connected parts
as may have become incorporated with it; and hence, to the botanist,
a boll of cotton, a tickseed, or a cocklebur is just as much a fruit
as a peach or a watermelon.
=283. Classification of fruits.=—For convenience of description,
fruits are classed as:
(_a_) Dry or fleshy, according as they have a more or less hard and
bony, or soft and fleshy, texture.
(_b_) Dehiscent, or indehiscent, according as they open at maturity
in a regular way to discharge their seed, or remain closed until the
covering wears away or is burst by the germinating embryo.
Fleshy fruits are very seldom dehiscent, though some few, as the
balsam apple and the chayote, or one-seeded squash, discharge their
seed when mature. The banana and some other fleshy fruits, when
peeled, separate along regular lines, and in this respect behave very
much as if they were fleshy pods.
=284. When is a fruit ripe?=—A fruit is ripe horticulturally, when
it is good to eat; it is ripe botanically, when it has set its seed.
Many of our choicest table fruits, such as the pineapple, banana, and
most varieties of fig, seldom are botanically ripe, since they rarely
produce perfect seeds.
It is the constant effort of the horticulturist to develop those
parts of a plant that are useful to man, while in a state of nature
the plant seeks to develop such parts as best serve its own purpose
in the struggle for existence. The plants most useful to man have,
as a general thing, been subjected to a long course of artificial
breeding and selection. They are forced developments, often
monstrosities, from the plant’s point of view, if we could conceive
of it as capable of having an opinion. Nature is continually striving
to reclaim them; and if left to themselves, they must either obey
“the call of the wild,” or die out.
[Illustration: FIG. 366.—A seedless citrange, hybrid between the
orange and the lemon.]
=285. Seedless fruits and vegetables.=—As the seed is the most
important thing to the plant, the edible parts in wild fruits are, as
a rule, subsidiary to its development. In a state of nature, fruits
will generally wither and drop from the stem, if for any reason they
have become incapable of perfecting their seed. It is only in a few
kinds, limited to those which can successfully propagate themselves
by other means, that the production of seed does not take place.
Among cultivated species, however, where propagation is carefully
provided for by man, the seed is of less importance, and sterile
varieties that might soon die out under natural conditions, continue
their existence indefinitely under his fostering hand. The seeds
of edible fruits are, as a general thing, both indigestible and
unpalatable (21), and hence the efforts of the horticulturist are
directed largely to getting rid of them, or to very greatly reducing
their size and number in proportion to the edible parts.
=286. How seedless fruits arise.=—The perfecting of seed requires a
great consumption of food and energy on the part of the plant, and
when it is led, for any reason, to expend an unusual amount of force
in some other function,—as for instance, in producing tubers or in
growing bulbs,—it is apt to bear few seeds and to depend more or less
completely upon other methods of reproduction.
Among cultivated plants, selection on the part of man, whether
conscious or unconscious, has perhaps contributed more than any
other cause to bring about the same result. To this agency is
probably due the development of our common domestic fig, of which
over four hundred varieties that mature fruits without fertilization
are cultivated in the United States alone. The fig was one of the
earliest fruits known to cultivation; and the early navigators,
ignorant of the processes of fertilization, would naturally, in
choosing specimens to carry home with them, select only fruit-bearing
trees. Such of these as matured fruits would be preserved and
propagated, until, by repeated selection, hundreds of edible
varieties have been developed that ripen fruits without caprification
(279).
=287. The use of the fruit to the plant.=—The object of the fruit is
to furnish protection to the seeds during their period of development
and inactivity, and to aid in various ways the work of dispersal.
It probably takes part also in digesting and diffusing nourishment
for the use of the developing seeds. It has been shown in previous
chapters that plants, almost without exception, are in the habit of
storing up food in various ways as a provision for fruiting. That a
large portion of the stored nourishment is used up in the performance
of this function is proved by its disappearance from those parts—for
example, from fleshy roots, such as beets and turnips, after they
have “gone to seed.”
Practical Questions
1. What is the use of the down on the peach? The bloom of the plum
and grape? [202, (1); Exp. 91.]
2. Why are apples, pears, plums, and other fleshy fruits nearly
always rosier on one side than on the other? (Exp. 90.)
3. Can annuals be improved in any other way than by seed selection?
4. Would a seedless annual be perpetuated under natural conditions?
5. Why is decrease of moisture and increase of light desirable as
the fruiting season approaches? (126, 127; Exp. 90.)
6. Why are turnips, carrots, and other fleshy roots unfit to eat if
left over till the plants have seeded? (92, 287.)
II. FLESHY FRUITS
MATERIAL.—A specimen of each of the four principal kinds of fleshy
fruits. Examples of the pome are: apple, pear, quince, rose hip,
haw; of the berry: grape, tomato, cranberry, currant, gooseberry,
lemon; of the pepo: melon, squash, pumpkin; of the drupe: peach,
plum, cherry, dogwood. Specimens of the commoner kinds can nearly
always be found in the market; if nothing better is available,
pickled and dried ones may be used—figs, prunes, dates, raisins,
etc.
[Illustration: FIG. 367.—Outside of an apple, showing lenticels on
the skin.]
=288. Dissection of a pome fruit.=—Examine with a lens the outside of
an apple or a pear. Can you make out the lenticels? What difference
in color do you notice between the ripe and unripe fruit? What
difference in taste? What substance would you judge from this, do
ripe fruits contain which green ones do not? Test both kinds for
sugar and starch; which contains the more of each? Strictly speaking,
sugar and starch are merely different forms of the same chemical
compound. In ripe fruits the starch has been cooked by the sun and
converted into sugar.
With the point of a pencil separate the little dry scales that cover
the depression in the center of the fruit at the end opposite the
stem. How many of them are there? How does this accord with the
plan of the flower as outlined in 229? They are the remains of the
sepals, as will be more apparent on comparing them with the larger
and more leaflike ones on a hip, which is clearly only the end of the
footstalk enlarged and hollowed out with the calyx sepals at the
top. Cut a cross section midway between the stem and the blossom end,
and make an enlarged sketch of it. Label the thin, papery walls that
inclose the seed, _carpels_. How many of them are there, and how many
seeds does each contain? The carpels, together with all that portion
of the fruit which surrounds and adheres to the ovary, constitute
the _pericarp_, or wall of the seed vessel. The fleshy part of the
apple is no part of the ovary proper, but consists merely of the
receptacle, or end of the footstalk, which becomes greatly enlarged
and thickened in fruit. Look for a ring of dots outside the carpels,
connected (usually) by a faint scalloped line. How many of these dots
are there? How do they compare in number with the carpels? With the
remnants of the sepals adhering to the blossom end of the fruit?
[Illustration: FIG. 368.—Cross section of a pome: _pl_, placenta;
_c_, carpels; _f_, fibrovascular bundles.]
[Illustration: FIG. 369.—Vertical section of a pome: _p_, peduncle;
_f_, fibrovascular bundles; _s_, seeds; _pl_, placenta; _c_, carpel.]
Next make a vertical section through a fruit, and sketch, enlarging
it sufficiently to show all the parts distinctly. Observe the line of
woody fibers outside the carpels, inclosing the core of the apple.
Compare this with your cross section; to what does it correspond?
Where do these threads originate? Where do they end? Can you make
out what they are? (176.) Notice how and where the stem is attached
to the fruit. Label the external portion of the stem, _peduncle_;
the upper part, from which the fibrovascular bundles branch, the
_receptacle_. It is the enlargement of this which forms the fleshy
part of the fruit. Try to find out, with the aid of your lens and
dissecting pins, the exact spot at which the seeds are attached to
the carpels, and label this point, _placenta_. Notice whether it is
in the axis where the carpels all meet at their inner edges, or on
the outer side. Observe, also, whether the seed is attached to the
placenta by its big or its little end. If you can find a tiny thread
that attaches the seed to the carpel; label it, seed stalk. Fruits
of this kind are classed, botanically, as _pomes_. Write, from your
analysis, a definition of the pome.
[Illustration: FIGS. 370, 371.—Enlarged receptacle of Carolina
allspice (_Calycanthus_), containing fruits attached to its inner
surface: 370, exterior; 371, vertical section.]
=289. Modifications of the receptacle.=—Compare with the drawings
you have made, a haw and a hip. What points of agreement do you see?
What differences? Which of the two more closely resembles the typical
pome? The receptacle is subject to a variety of modifications,
and forms a part of many fruits, for example, the fig, lotus, and
calycanthus (Figs. 370, 371); but a fruit is not a pome unless the
containing receptacle becomes more or less soft and edible.
=290. The pepo, or melon.=—Next examine a gourd, cucumber, squash, or
any kind of melon, and compare its blossom end with that of the apple
or pear. Do you find any remains of a calyx, or other part of the
flower? Examine the peduncle and observe how the fruit is attached
to it. Can you tell what made the outer epidermis of the rind? Put
a small piece under the microscope; do you see any stomata, or
lenticels? Cut cross and vertical sections, and sketch them, labeling
each part. There may be some difficulty in making out the carpels,
for they are not separate and distinct as in the pome, but confluent
with the enlarged receptacle, which in these fruits forms the outer
portion of the rind, and also with each other at their edges, so
as to form one unbroken circle, as if they had all grown together.
And this is precisely what has happened. The placentas are greatly
enlarged and modified, and it may be necessary to refer to the
diagram, Fig. 372, _c_, in order to make them out. How many locules,
or chambers, are there in your specimen? How many placentas? Notice
that these are central and double, but extend to the pericarp before
dividing so that they appear to be parietal, and twice their real
number, which is only three. Are the seeds vertical, as in the apple,
or horizontal? Look for the little stalk, or thread, that attaches
them to the placenta.
_Pepo_ is the name given by botanists to this kind of fruit. Write in
your notebook a proper definition of it, from the specimens examined.
[Illustration: FIG. 372.—Cross section of gourd: _c_, one of the
carpels in diagram. (_After_ GRAY.)]
[Illustration: FIGS. 373, 374.—A potato berry: 373, exterior; 374,
cross section.]
=291. The berry.=—Examine a tomato, an eggplant, a grape, cranberry,
lemon, or orange, in both cross and vertical section, and compare
it with the melon and the apple. What differences and resemblances
do you find? Cut a cross section, and draw, showing the attachment
of the seeds. How many locules are there? Normally the tomato is a
two-celled fruit, like the potato berry (Fig. 374), but it has been
so modified by cultivation that the original plan is not always easy
to distinguish. See if you can make it out. Do the seeds in your
specimen appear to be healthy and well developed, or are some of them
small and aborted? How do you account for this? (285, 286.) What
difference do you notice in color between the ripe and unripe fruit?
Write a definition of the berry from the study you have made of it.
Berries are the commonest of all fleshy fruits, and the most variable
and difficult to define. In general, any soft, pulpy, or juicy mass,
like the grape and tomato, whether one or many seeded, inclosed in
a containing envelope, whether skin or rind, is a berry. Its typical
forms are such fruits as the grape, mistletoe, pokeberry, etc.,
though such diverse forms as the eggplant, persimmon, red pepper,
orange, banana, and pomegranate have been classed as berries; and, in
fact, the melon and the pumpkin are only greatly modified kinds of
the same fruit. In popular language, any small, round, edible fruit
is called a berry. This is a good commercial classification, though
not botanically correct.
[Illustration: FIG. 375.—Vertical section of a drupe. (_After_ GRAY.)]
=292. The drupe, or stone fruit.=—Examine a section of a green plum,
peach, or cherry, before the stone has hardened, and tell from what
part it is formed. This stony covering, composed of the inner layer
of the pericarp, and enveloping the seed like an outer coat, is the
main distinction between the drupe and the berry, but it is not
always possible to make out its real nature except by an examination
of the young ovary. In a green drupe, before the stone has hardened,
its connection with the fleshy part is very evident, and the ripe
fruit will answer inquiries if we know how to put them. Open the
stone, and the seed will be exposed with its own coverings inside.
When a stone has more than one kernel,—for instance, an almond or
peach stone, —the stone is not a seed coat, but the hardened inner
wall of a seed vessel or ovary; for a seed coat can never contain
more than one seed, any more than the same skin can contain more than
one animal.
All the fruits considered in this section belong to the fleshy class.
These form the bulk of the fruits sold in the market, and are of
special importance to the horticulturist.
Practical Questions
1. Is the tomato horticulturally a fruit or a vegetable? the
squash? eggplant? cranberry? olive? elderberry? pepper? date?
maypop? crab apple? black haw? To what class does each belong?
(283, 288-292.)
2. Of what use to the plant is the hard stone of the drupe? (21.)
3. Is the pulp of fleshy fruits agreeable to the taste before they
are ripe? After? What advantage is this to the plant? (21.)
4. Are the seeds of edible fruits, as a general thing, digestible
or agreeable to the palate?
5. Is this an advantage to man? To the plant? (21, 284, 285.)
6. What are the most common fleshy fruits in autumn?
7. With what vegetative parts of the plant does the skin of many
fruits present correspondences? Are these such as to indicate
homology, or analogy only, between them? (100, 118, 288, 289; Exp.
89.)
8. Name six of the most watery fruits that grow in your
neighborhood.
9. Under what conditions as to soil, heat, moisture, etc., does
each thrive best?
10. Would a gardener act wisely to infer that because a fruit
contains a great deal of water it should be planted in a very wet
place?
11. Which contains more water, the fruit or the leaves of the apple?
12. Why does not the fruit, when separated from the tree, wither as
quickly as do the leaves? (Exp. 91.)
III. DRY FRUITS
MATERIAL.—Some easily attainable specimens of dry fruits are (1)
nuts: acorn, hickory nut, walnut, chestnut, pecan, filbert; (2)
pods: pea and bean pods, capsules of larkspur, milkweed, jimson
weed, cotton; (3) grains: corn, wheat, oats, rice; (4) akene:
sunflower, thistle, dandelion, buckwheat, clematis.
=293. Importance of dry fruits.=—Dry fruits are not in general so
conspicuous or so attractive as fleshy ones, but on account of their
great number and variety they offer a wide field for study. They are
also of great interest from an economic point of view: (1) because
they include the cereal grains that furnish so large a portion of our
food, and (2) because the greater part of the troublesome weeds that
infest our crops are scattered by fruits of this class.
=294. Indehiscent fruits.=—These kinds are so simple that it will not
be necessary to give much time to them. Compare an acorn, a chestnut,
or a filbert with a ripe bean pod or with a capsule of morning-glory.
Try to open each with your fingers; which _dehisces_, or opens, the
more readily? Which is indehiscent, having no regular way of opening?
How many seeds or kernels do you find in the dehiscent pod? How many
in the indehiscent one? Would it be of any advantage for a one-seeded
pod to open? Remove the kernel from the indehiscent fruit; has it any
covering besides the shell? Which is the pericarp, and which the seed
coat?
[Illustration: FIGS. 376, 377.—Nut of the pecan tree: 376, exterior;
377, cross section.]
[Illustration: FIGS. 378, 379.—Nutlike seeds: 378, horse-chestnut;
379, seed of the fetid sterculia.]
=295. The nut= is easily recognized by its hard, bony covering,
containing usually, when mature, a single large seed that fills
the interior. Care should be taken not to confound with true nuts,
large bony seeds, like those of the buckeye, horse-chestnut, date,
and the Brazil nut sold in the markets. In the true nut, the hard
covering is the seed vessel, or pericarp, and not a part of the seed
itself, though it often adheres to it so closely as to seem so. In
bony seeds, like those of the horse-chestnut and persimmon, the hard
covering is the outer seed coat. The distinction is not always easy
to make out unless the seed can be examined while still attached to
the placenta of the fruit.
[Illustration: FIGS. 380, 381.—Akenes (magnified): 380, of buckwheat;
381, of cinque-foil.]
[Illustration: FIGS. 382-384.—Cremocarps, fruits of the parsley
family.]
=296. The akene=, of which we have examples in the tailed fruit of
the clematis, the tiny pits on the strawberry, and the so-called
seeds of the thistle, dandelion, and sunflower, is a small, dry,
one-seeded, indehiscent fruit, so like a naked seed that it is
generally taken for one by persons not acquainted with botany. It
is the commonest of all fruits, and there are so many kinds that
special names have been applied to some of the most marked varieties.
The akene of the composite family may generally be known by the
various appendages in the form of scales, hooks, hairs, or chaff,
that crown it (Figs. 309-314). The fruits of the parsley family are
merely a sort of double akene attached by the inner face to a slender
stalk from which it separates at maturity.
The _samara_, or key fruit, is an akene provided with a wing to
aid in its dispersion by the wind. The maple, ash, and elm furnish
familiar examples.
[Illustration: FIGS. 385, 386.—Samaras: 385, ailanthus; 386, maple.]
[Illustration: FIGS. 387, 388.—Grain of wheat with husks on: 387,
front view; 388, back view.]
=297. The grain=, so familiar to us in all kinds of grasses, is
economically the most important of all fruits. It is popularly
classed as a seed, and for practical purposes may be treated as such,
but it is really a modification of the akene in which the seed coats
have so completely fused with the pericarp that they can no longer be
distinguished as separate organs. Peel the husk from a grain of corn
that has been soaked for twenty-four hours, and you will find the
contents exposed without any covering; remove the shell of an acorn
or a hickory nut, and the seed will still be enveloped by its own
coats. Would it be of any advantage for the seed of an indehiscent
fruit, like a grain of corn or oats, to have a separate special
covering of its own?
[Illustration: FIG. 389.—Follicle of milkweed.]
[Illustration: FIG. 390.—Leaflike follicle of Japan varnish tree:
_S_, outer (dorsal) suture; _S′_, inner (ventral) suture.]
=298. Dehiscent fruits.=—_Pod_, or _capsule_, is the general name
applied to all dehiscent fruits. The simplest possible kind of pod
is the _follicle_, composed of a single carpel, like those of the
larkspur, milkweed, and marsh marigold, and may be regarded as a
modified leaf. Examine one of these pods and you will find that
it splits down one side, which corresponds to the edges of the
leaf brought together and turned inward to form a placenta for the
attachment of the seed. This line of union is called a “suture,” from
a Latin word meaning a “seam.”
=299. The legume.=—Get a pod of any kind of bean or pea, and observe
that it differs from the follicle in having two sutures or lines
of dehiscence. One of these runs along the back of the carpel and
corresponds to the midrib of the leaf; the other, corresponding to
the united edges of the carpellary leaf, always turns inward, toward
the axis of the flower, and forms the placenta.
[Illustration: FIGS. 391-393.—Legumes: 391, legume of bean: _v_,
ventral suture; _d_, dorsal suture; 392, constricted legume of senna
(_Cassia Nelsonia_); 393, legume of a pea, with partially constricted
pod.]
[Illustration: FIG. 394.—Loment of beggar-ticks.]
The beggar-ticks, so unpleasantly familiar to most of us, are merely
a kind of legume constricted between the seeds and breaking up into
separate joints at maturity. What kind of indehiscent fruits do the
joints become when separated? (296.)
[Illustration: FIG. 395.—Cross section of one-celled syncarpous
capsule of frostweed, with parietal placentæ. (_After_ GRAY.) FIG.
396.—Follicles of larkspur borne on the same torus, but distinct.]
=300. Compound or syncarpous pods.=—The carpellary leaves may unite
either by their open edges, as if a whorl like that represented in
Fig. 188 were to grow together by the margins (Fig. 395); or each
may first roll itself into a simple follicle like the larkspur
and columbine (Fig. 396), and then a number of these may unite by
their ventral sutures into a single syncarpous capsule, with as
many locules as there are carpels (Fig. 398). The seed-bearing
sutures being all brought together in the center, the placenta
becomes _central_ and _axial_. In the first case (Fig. 395) the open
carpels form a one-chambered capsule, though the placentas sometimes
project, as in the cotton, so far as to produce the effect of true
partitions with a central axial placenta. In capsules with only one
compartment, the number of carpels can generally be determined by the
number of sutures or of placentas.
[Illustration: FIG. 397.—Pods of Echeveria, contiguous, but distinct.]
[Illustration: FIG. 398.—Capsule of Colchicum, with carpels united into
a syncarpous pod.]
[Illustration: FIG. 399.—Capsule of corn cockle, with free central
placenta.]
Practical Questions
1. To what class of fruits does each of the following belong—rice;
beggar-ticks; poppy; peanut; jimson weed; chinquapin; caraway?
2. Is the coconut, as usually sold in the market, a fruit or a seed?
Suggestion: carefully examine the “eyes,” from without and from
within; if you can get a specimen with the husk on, it will help to
a decision.
3. Can you name any syncarpous, or compound capsule, that is
single-seeded?
4. Can you name any indehiscent fruit that has normally more than
one seed?
5. Give a reason for the difference. (23.)
6. Name the weeds of your neighborhood that are most troublesome on
account of their adhesive fruits.
7. Do these fruits belong, as a rule, to the dehiscent or to the
indehiscent class?
8. Give a reason for the difference, if any is noted. (23.)
IV. ACCESSORY, AGGREGATE, AND MULTIPLE FRUITS
MATERIAL.—For autumn and winter, examples of accessory fruits are:
pineapple, common apple, pear, rose hip; aggregate: magnolia,
tulip tree, wild cucumber, sweet flag (_Calamus_); multiple: osage
orange, sweet gum balls, pine cones, figs, fresh or dried.
For spring and summer, examples of accessory fruits are: raspberry,
strawberry, squash, cucumber; aggregate: strawberry, blackberry,
Jack-in-the-pulpit; multiple: fig, mulberry. Most of those named
will be found to belong to more than one class; the strawberry, for
instance, is both accessory and aggregate; the fig and pineapple,
accessory and multiple.
=301.= Besides the varieties already named, all fruits, whether
fleshy or dry, may be simple, accessory, aggregate, or collective.
Fruits of the first kind need no explanation; they consist merely
of a single ripened ovary, whether of one or more carpels, as the
peach, cherry, bean, and lemon.
[Illustration: FIGS. 400, 401.—Vertical sections showing the relation
between a strawberry flower and fruit: 400, the flower; 401, the
fruit developed from it. The corresponding parts are indicated by
connecting lines; _r_, receptacle; _a_, sepal; _b_, petal; _s_,
stamens; _c_, carpel (akene in fruit); _p_, style of the pistil;
_pl_, pulp of the fruit.]
=302. Accessory fruits= are so called because some other part than
the seed vessel, or ovary proper, is coherent with, or accessory to
it, in forming the fruit, as in the apple and the hip. The accessory
part may consist of any organ, but is more frequently the calyx or
the receptacle. In the strawberry, the little hard bodies, usually
called seeds, that dot the surface are the true fruits (akenes). A
vertical section through the center will show the edible part to
consist wholly of the enlarged receptacle. In the pineapple, the
edible stalk may be traced through a mass of flowers whose seed
vessels have become enlarged and ripened into fruits.
=303. Aggregate fruits.=—Some accessory fruits, the strawberry and
blackberry for example, are, at the same time, aggregate; that is,
they are composed of a number of separate individual fruits produced
from a single flower. The cone of the magnolia and of the tulip tree
are aggregate fruits; can you name any others?
[Illustration: FIGS. 402-404.—Multiple fruit of the pineapple: 402,
external view of a ripe fruit, showing the prolonged receptacle
growing into a new plant above, and the scaly bracted covering below;
403, vertical section through the axis of a fruit, showing _a_, the
receptacle, with _b_, _b_, the fleshy ovaries cohering around it
and forming the edible part of fruit; 404, a single “eye” or scale,
somewhat reduced, showing the scaly bract from the axil of which the
(generally) abortive flower originates.]
=304. Collective, or multiple, fruits.=—The pineapple is an example
of both an accessory and a multiple fruit, being composed of the
ripened ovaries of a number of separate flowers that have become
more or less coherent. The osage orange, sweet gum balls, fig, and
mulberry are other examples of this class.
=305. Dissection of a multiple fruit.=—Get one of the dried figs sold
by the grocers. Look at the small end where the skin originates; of
what part is it a modification? (289.) Can think of a reason for this
curious, urnlike enlargement of the receptacle? Is there anything
about the fig, for instance, that renders it peculiarly liable to be
preyed upon by birds and insects? Could any but a very small insect
get through the eye without injuring the fruit? Could it free itself
from the sticky mass inside and get out again without difficulty?
Would you judge from this that the caprification of the fig is easily
effected (279), even when the fig wasp is present? Can you now
account for the fact that over four hundred varieties of cultivated
figs ripen their fruit without fertilization?
[Illustration: FIG. 405.—Vertical section of a fig, showing the
minute flowers inside the closed receptacle.]
Open your specimen and examine the contents; what do you find? From a
dried specimen it will hardly be practicable to make out clearly that
the pulp of the fig consists of hundreds of tiny pistillate blossoms
that line the inner face of the receptacle. The little grains
usually taken for seeds are really small akenes—the ripened ovaries
of flowers that have been pollinated from the caprifig (279, 286).
Crush one gently and examine with a lens, or under a low power of the
microscope. It is these “botanically” ripe fruits (284) that give to
the dried figs of commerce their plumpness and their pleasant, nutty
flavor. Why are our native American figs lacking in these qualities
(279)? Could this defect be remedied? Do you know of any efforts
being made in that direction by American cultivators?
[Illustration: FIGS. 406-409.—Non caprificated and caprificated
figs: 406, outside appearance of non caprificated fig; 407, outside
appearance of caprificated fig; 408, interior of caprificated fig;
409, interior of non caprificated fig.]
=306. Fruit clusters.=—Be careful not to confound aggregate and
collective fruits with mere clusters, like a bunch of grapes or of
sumac berries. The distinction is not always easy to make out. The
clump of akenes that make up a dandelion ball, for instance, though
held on a common receptacle, like the mulberry and other collective
fruits, have so little connection with each other, and separate
so completely at maturity, as to partake more of the nature of a
cluster than of a collective fruit. The same is true of the clump
of tailed akenes that make up the fruit of the clematis. Though the
product of a single flower and thus technically an aggregate fruit,
they are really only a compact head or cluster. Some degree of
cohesion is necessary to constitute a cluster of matured ovaries into
an aggregate or a multiple fruit.
=307. The individual fruits= that make up the various kinds just
described may belong to any of the classes mentioned in the two
preceding sections: those of the blackberry, for instance, are
drupes; of the strawberry, akenes; of the sweet gum, capsules.
Practical Questions
1. To what class of fruits would you refer the following: a banana;
a tickseed; a dewberry; a cocklebur; a string bean; a watermelon;
a cantaloupe; a pomegranate; a black haw; a dogwood berry; a red
pepper?
2. Tell which of the following are aggregate or multiple fruits,
and which are fruit clusters: an ear of corn; of wheat; a
buttonwood or a sycamore ball; a hop; a dewberry; a pine cone; a
prickly pear. (303, 304, 306.)
3. Tell the nature of the individual fruits composing the different
combinations mentioned in the last question.
4. Can you suggest any advantage that might accrue to a species
from having its fruits clustered or compound? (21, 23, 24, 287.)
Field Work
1. Study the various edible fruits of your neighborhood with regard
to their means of dissemination and protection. Consider the object
of the protective adaptations in each case, whether against heat,
cold, moisture, animals, etc. Notice the color of the different
kinds, and trace its significance; for example, the bright red of
the holly, the dull color of muscadine, black haw, and wild smilax.
Account for the prevalence of red among autumn fruits. Notice the
position of the fruit on the bough and explain its object; as, for
instance, the clustering of dogwood at the end of the twig, the
pendent position of grapes and honey locusts. Observe the relation
between the color and size of fruits and their grouping. What
advantage is it for sumac and bird haws to be gathered in large
clusters?
2. Compare wild with cultivated fruits and notice in what respects
man has altered the latter for his own benefit. Note, for instance,
the difference between cultivated apples and the wild crab, between
the cultivated grains and wild grasses. Observe the great number of
varieties of each kind in cultivation and try to account for it.
3. Notice the situations in which different kinds of fruits
grow, whether hot, dry, moist, windy, or sheltered, and how they
are affected by their surroundings. For example, account for
the difference between blackberries growing on a dry hillside,
and those in moist land along the borders of a stream. Give the
conclusions drawn from your observations in each case.
4. Notice what animals feed upon the different kinds, and whether
their visits are harmful or beneficial. Consider in what respects
the interests of the plant itself, the interests of man, and the
interests of other animals may clash or coincide. Examine the
vegetation along the hedgerows and borders of fields and old
fences. Notice the kind of plants that compose it—sumac, sassafras,
cedars, cat brier, etc. The list will be slightly different
for different localities, but this will not alter the general
conclusion. What kinds of fruits and seeds do these shrubs produce?
What kinds of living creatures frequent hedgerows and feed upon the
seeds of such plants? Do you see any relation between these facts
and one of the modes of seed dispersal?
5. Classify all the fruits you have collected during your
walk, under their proper heads, as fleshy or dry, dehiscent or
indehiscent, simple, accessory, aggregate, collective. Be careful
to distinguish between compact clusters, like the heads of clematis
or buttonwood, and truly compound fruits.