EFFECT OF MANGANESE COMPOUNDS
I. PRESENCE OF MANGANESE IN PLANTS
The presence of manganese as a constituent of plant tissues has been known
for many years, and in view of the close association between iron and
manganese it was natural that the early investigators should seek for the
latter element. De Saussure (1804) gives one of the earliest references to
manganese in plant ash, stating that it occurs in the seeds in less great
proportion than in the stems, and also that the leaves of trees contain
less in autumn than in spring. At first oxides of iron and manganese
were put together as “metallic oxides” and little or no attempt was made
to separate them so as to get an idea of their relative abundance. John
(1814) gives a number of rough analyses of plants and indicates the
presence of manganese in many plants, including _Solanum tuberosum_,
_Brassica oleracea viridis_ L., _Conium maculatum_, _Aesculus_ (in outer
bark), and _Arundo Sacchar_. No further references presented themselves
until 1847, as probably manganese was overlooked and always classed with
iron in any analyses made during that time. Kane (1847) found traces of
manganese in the ashes of some samples of flax, but none in others, and
examinations of the soils on which the plants were grown gave similar
results. Mayer and Brazier (1849) confirmed this result. Herapath (1849)
analysed the ashes of various culinary vegetables, finding manganese in
cauliflowers, swede turnips, beetroot, and in one variety of potato (Forty
fold).
Malaguti and Durocher (1858) tried to investigate the matter
quantitatively. The oxides of iron, manganese, and aluminium were all
classed together, and the mean percentage of the three varied from
·85%–5·06% according to the varieties of plants concerned, Cruciferae
possessing least and Leguminosae most. Different mean results with the
same plant were obtained from different soils.
Wolff (1871) made other quantitative analyses including _Trapa natans_
(·15% Mn₃O₄), _Acorus Calamus_ (1·52% Mn₃O₄), _Alnus incana_ (trace–·73%
Mn₃O₄), _Pyrus communis_ (2·15% Mn₃O₄). Many other plants were mentioned
by Wolff as containing manganese.
Campani (1876) found manganese in ash by a method in which it was detected
as phosphate of manganese, and he claimed to be the first to discover
manganese in wheat ash. Warden (1878) found traces of Mn₃O₄ in the ash of
opium from Behar.
Dunnington (1878) detected manganese in the ash of wheat, ·00144 gm. (as
Mn₃O₄?) in 300 grams of “Dark Lancaster” variety, equivalent to ·027% of
the pure ash. The ash was exhausted with nitric acid, and after separating
the iron the ammonium sulphide precipitate was found to contain manganese,
and gave by fusion with nitre and sodium phosphate a violet coloured mass.
Andreasch (1878) found slight traces of Mn₃O₄ in the flowers of _Dianthus
caryophyllus_, none occurring elsewhere, while in _Rosa remontana_ it
appeared in both leaves and flowers.
Maumené (1884) tested many food plants and concluded that some quantity
of manganese is frequently present in potato, rice, barley, carrot,
lentil, pea, beetroot, asparagus, chicory, most fruits, tea, and also in
some fodder plants, as lucerne, oats, and sainfoin. Ricciardi (1889),
Hattensaur (1891) also added to the list of plants proved to contain
manganese. Guerin (1897) studied the manganese content of woody tissues.
Sawdust was treated with distilled water containing 1% caustic potash,
expressed, and filtered after two or three days. A brown coloured liquid
was obtained, which when treated with a slight excess of hydrochloric acid
gave an abundant flocculent precipitate. This precipitate proved to be
soluble in pure water, so it was washed with slightly acidulated distilled
water, and after further purification was analysed. No trace of iron was
obtained, but about ·402% Mn was found. Guerin regarded the precipitate
as a “nucleinic” combination, which he supposed to occur generally in wood
and to contain the manganese present in the woody tissues of all plants.
Schlagdenhauffen and Reeb (1904) detected manganese in a petrol extract
of such cereals as barley, oats, and maize, and since inorganic salts
of manganese are not soluble in such liquids as ether or petrol they
concluded that the manganese must be present in the plant in organic
combination, thereby upholding Guerin’s view. Loew and Seiroku Honda
(1904) give a table of Mn₃O₄ in the ashes of certain trees. This is very
high in some cases, rising to 11·25% in the ash of beech leaves, 6·73% in
birch leaves, and 5·48% in chestnut fruits.
Gössl (1905) gives lists of the distribution of manganese in plants, both
Thallophytes and Phanerogams, indicating the presence of much or little of
the element. As a rule, he states, marsh and water plants gather up more
manganese than do land plants.
The Gymnosperms seem to be particularly rich in their manganese content.
Schröder (1878) tested for the element in firs and pines and found the
following amounts of Mn₃O₄.
In 100 parts ash. In 1000 parts dry matter.
Fir Pine Fir Pine
33·18 13·46 2·76 ·77
He gave a table of detailed analyses showing the differing proportions of
manganese in the different parts of the fir.
Baker and Smith (1910) paid special attention to manganese in their
exhaustive work on the Pines of Australia. They state that “in the
anatomical investigations of the timber, bark, and leaves of the various
species, there was found to be present, in a more or less degree, a
naturally brownish-bronze coloured substance, which invariably stained
dark brown or almost black with haematoxylin.” This substance on careful
investigation proved to be a compound of manganese. The quantity present
varies with the species and also with the plant organs. The different
species of the genus Callitris show variable percentages of manganese
from a maximum of 0·230% in _C. gracilis_, to a minimum of 0·010% in _C.
robusta_. The percentage of manganese in Australian Coniferae other than
Callitris is given by the authors in the following table:
Ash of timber of Agathis robusta 0·145% Mn.
„ „ Araucaria Cunninghamii 0·054% „
„ „ Araucaria Bidwilli 0·077% „
„ „ Actinostrobus pyramidalis 0·077% „
„ „ Podocarpus elata 0·002% „
„ „ Dacrydium Franklini 0·129% „
„ „ Athrotaxis selaginoides 0·019% „
„ „ Phyllocladus rhomboidalis 0·145% „
Air-dried black gum of Agathis robusta 0·0046% „
„ „ Araucaria Cunninghamii 0·0038% „
Baker and Smith assume that manganese is essential to the production
of the most complete growth of Coniferae. The element is found in these
plants even when they grow on soils containing only traces of manganese
and it is suggested that possibly the excess or deficiency of manganese
in the soil helps to govern the location of certain of the Australian
Coniferae. The authors conclude that manganese may be essential to the
growth of these plants, and that its association with plant life may be
considered to date back to past geological time, as is indicated by plates
illustrating fossil woods.
II. EFFECT OF MANGANESE ON THE GROWTH OF HIGHER PLANTS.
1. _Toxic effect._
(_a_) _Toxic action of manganese compounds in the presence of soluble
nutrients._
Little work seems to have been done on the action of manganese compounds
in water cultures. Knop (1884) just indicated that manganese compounds had
no effect on maize, but gave no details. Japanese investigators touched
on the matter in the course of their extensive experiments with this
element. Asō (1902) found that the greater concentrations of manganese
sulphate exercised an injurious influence on barley. Even in solutions
with as little as ·002% manganese sulphate (= 1/50,000 MnSO₄) the roots
gradually turned brown, the lower leaves following suit. The brown colour
was concentrated at certain points of the leaves, and microscopical
examination showed that the membranes of the epidermal cells, and in some
cases the nuclei, were stained deeply brown. The greatest concentration
endured by barley without injury seemed to be about ·01 per 1000 =
1/100,000. The presence of iron in the food solutions seems to counteract
the effect of the manganese to some extent by delaying the yellowing of
the leaves. Wheat proved very similar to barley in its reactions, though
more iron is necessary to give good healthy growth. Asō states that
wheat is able to overcome the injurious action of manganese much more
readily than is barley. With peas the yellowing of the leaves was delayed,
probably on account of a sufficient supply of iron in the reserve stores
of the seeds.
Loew and Sawa (1902) found that ·25% = 1/400 MnSO₄ (anhydrous) kills pea
plants within five days and that the green colour is gradually affected
with more dilute solutions. Barley and soy beans were grown in nutritive
solutions with either iron sulphate or manganese sulphate or both (·01%
FeSO₄, ·02% MnSO₄, ·01% FeSO₄ + ·02% MnSO₄). At first the growth was
increased by the action of two salts together, but eventually the shoots
turned yellowish, and assimilation was depressed, so that decreased
nutrition led to relaxation in the speed of growth, indicating the toxic
action due to the manganese sulphate.
The Rothamsted experiments supported Asō’s work on the action of manganese
sulphate on barley, concentrations of the salt above 1/100,000 having a
retarding influence on the growth, the roots being coloured brown and
the leaves also showing discolouration. At an early stage in growth
the lower leaves of the plants receiving the most poison began to be
flecked with brown spots, which were at first attributed to an attack
of rust. Suspicion was soon aroused, however, and a closer microscopic
investigation showed that no disease was present, but that the cells
in the affected spots were dead and brown, though they retained their
shape. The dead cells at first occurred in small patches, which spread
and coalesced until ultimately the whole leaf was involved. Some of the
affected leaves were detached and fused with a mixture of sodium carbonate
and potassium nitrate. On dissolving up the resulting mass with water
a green colouration was obtained, indicating the presence of manganese
in the leaves. This shows that the manganese is taken up by the roots,
transferred to the leaves and then deposited in them, the lower leaves
being the first affected.
The presence of manganese in the nutritive solution retarded the ripening
of the grain to some extent, as when the grains from the control plants
were hard and ripe, those from plants treated with 1/10,000 MnSO₄ were
green, those with 1/100,000 were a mixture of ripe, half-ripe, and green
grains, while plants which had received 1/1,000,000 MnSO₄ possessed ripe
grains.
Peas give similar results to barley so far as the vegetative growth is
concerned, the same retardation with the higher concentrations being
observed, while the brown discoloured patches in the lower leaves are
much in evidence. All traces of manganese in the leaves disappear when the
concentration falls to 1/250,000. On the whole peas are more sensitive to
manganese poisoning than is barley, and the higher strengths of manganese
prove more deleterious to them.
(_b_) _Toxic action of manganese compounds in sand cultures._
Little work has been done on this aspect of the problem. Prince de Salm
Horstmar (1851) grew oats in sand with various combinations of nitrogenous
substances and inorganic mineral salts. He stated that until the time of
fruit formation manganese does not seem to be essential to the oat unless
iron is in excess in the substratum.
(_c_) _Toxic action of manganese compounds in soil cultures._
A large body of work has been done with manganese in soil cultures, but
the toxic effect is hardly indicated, possibly because it is less manifest
under soil conditions, possibly because the observation of the toxic
action has been almost completely overshadowed by the interest in the
stimulation observed under the same circumstances. Namba stated that ·5
gm. MnSO₄ added to 8 kgm. Japanese soil exerted a depressing influence
on the growth of various plants. The Hills Experiments (1903) indicated
some toxic effect. Various soluble and insoluble salts of manganese were
added to soil in pots at the rate of 2 cwt. per acre, wheat being sown.
On the whole the plants from untreated pots were as good as any with
manganese except those that received manganese nitrate or phosphate.
Manganese iodide distinctly retarded growth. The plants that grew did well
eventually, but development of the ear was greatly or entirely retarded.
If the seeds were soaked in the iodide, a concentration of 10% was found
to be harmful, 5% allowing normal growth. Similar experiments with barley
showed that plants treated with manganese carbonate and sulphate were both
inferior to the untreated plants; with iodide less plants were obtained
and their development was abnormal. Soaking the seeds in the iodide, even
in 10% solution, did not do damage as it did with wheat. The oxides were
apparently innocuous, but gave no increase either in corn or straw.
Kelley (1909) found that on soils in Hawaii in which excessive quantities
of manganese are present (5·61% Mn₃O₄) pineapples do not flourish,
but turn yellow and produce poor fruits, and also that if rather less
manganese is present (1·36% Mn₃O₄) the pineapples show the toxic effect
by yellowing during the winter months, but they recover completely during
the hot summer months. Kelley also observed that the deleterious effect is
hardly noticeable during the first twelve months of growth, and that after
a time a darkening occurs in the colour of the soil, which he attributes
to some change in the constitution of the manganese compounds.
Some interesting observations were made by Guthrie and Cohen (1910) on
certain Australian soils. A bowling green that was initially covered with
a healthy mat of couch grass developed a number of small patches after
about three years growth, on which the grass died off. No reason was
apparent for this phenomenon, as the cultural conditions were uniform and
to all appearances the soil over the whole area was similar in character.
Analyses of soil samples from the dead patches and from the neighbouring
healthy parts of the green showed that the chemical composition in both
cases was practically the same, except that while no manganese occurred in
the soil from the unharmed part, as much as ·254% Mn₂O₃ was found in that
from the dead patches. As no other differences were found it was argued
that the manganese, present in such large quantities, acted as a toxic
agent and killed off the grass. Other instances of manganese poisoning
in which wheat and barley were affected are quoted by these authors, the
analytical results indicating that possibly barley is able to withstand
without injury a greater quantity of manganese compounds in the soil than
is wheat.
2. _Effect of manganese compounds on germination._
Nazari (1910) rolled wheat grains in a paste of manganese dioxide,
iron sesquioxide (both with and without organic matter), and in what he
terms “artificial oxydases.” The seeds rolled in the last-named showed
the greatest energy in germination, while those with manganese gave
an appreciable acceleration. The presence of organic matter decreased
the action of manganese. The plants from the manganese seedlings gave
an increased yield in both straw and grain, while those treated with
sesquioxide of iron showed no gain over the check plants.
The Hills Experiments yielded some information as to the differing effects
of various compounds of manganese on germination. With wheat plants in
pot experiments manganese oxide (MnO₂) distinctly retarded germination
when applied at the rate of 2 cwt. per acre. With barley MnO₂, manganese
carbonate and sulphate all retarded germination, while with the iodide
50% of the seeds were entirely prevented from germinating.
3. _Does manganese stimulate higher plants?_
With manganese the evidence in favour of stimulation is more weighty than
with such poisons as copper, zinc and arsenic, and the literature on the
subject is correspondingly plentiful.
(_a_) _Stimulation in water cultures._
While Asō (1902) asserted that plants can develope normally in water
cultures in the absence of any trace of manganese, he further stated that
manganese compounds exercise both an injurious and a stimulant action on
plants. With increasing dilution of the compound the deleterious action
diminishes, while the stimulant action increases, and a dilution can be
reached in which only the favourable influence of the manganese becomes
obvious. The addition of ·002% manganese sulphate (= 1/50,000) to culture
solutions stimulated radish, barley, wheat and peas. The intensity of the
colour reaction of the oxidising enzyme of the manganese plants was found
to exceed that of the control plants, at least with regard to those leaves
on the manganese plants which had turned a yellowish colour.
Loew and Sawa (1902) obtained an initial increase of growth with
barley and soy beans in nutritive solutions + ·01% ferrous sulphate +
·02% manganese sulphate, but this initial stimulation was followed by
depression. These authors support Asō’s contention that manganese exerts
both an injurious and a stimulative action upon plants, and that the
promoting effect is still observable with manganese compounds in high
dilution, while the injurious effects disappear under this condition.
The Rothamsted experiments with barley show a decided stimulation with
1/100,000 MnSO₄ and less. Care was taken to utilise sublimed FeCl₃
to avoid error due to the introduction of manganese into the control
solution through the agency of this salt. It is interesting to notice that
concentrations that are weak enough to stimulate the vegetative growth
still show a depressing action in that they retard the ripening of the
grain, a fact which supports Loew and Sawa’s contention that manganese
exerts both a toxic and a stimulative action at one and the same time, the
balance showing itself according to the concentration (Fig. 17). In the
later experiments the plants were not allowed to form ears, but similar
results were obtained, except that when dealing with the vegetative growth
only, a definite stimulus was obtained with a higher concentration than in
those experiments in which the plants were allowed to form seed. This may
or may not be significant, as it is possible that seasonal variation and
individuality of the plants may have played some part. Barley seems to be
most extraordinarily sensitive to the action of manganese, as even 1 part
in 100,000,000 was found to exercise a beneficial action (Fig. 18). With
peas the evidence of stimulus is less well marked. No sign of stimulation
is obtained until a greater dilution is reached than is necessary with
barley. Even so the resulting curves are not sufficiently conclusive to
warrant the definite statement that manganese does act as a stimulant to
peas when present in very small quantities (Fig. 19).
[Illustration: Fig. 17. Curve showing the mean value of the dry weights
of ten series of barley plants grown in the presence of manganese sulphate
and nutrient salts. (Feb. 5th–March 29th, 1909.)]
[Illustration: Fig. 18. Photograph showing the action of manganese
sulphate on barley plants grown in the presence of nutrient salts. (Feb.
5th–March 29th, 1909.)
1. Control.
2. 1/10,000 manganese sulphate.
3. 1/100,000 „ „
4. 1/1,000,000 „ „
5. 1/10,000,000 „ „
6. 1/100,000,000 „ „ ]
[Illustration: Fig. 19. Photograph showing the action of manganese
sulphate on pea plants in the presence of nutrient salts. (Oct. 2nd–Dec.
20th, 1912.)
1. Control.
2. 1/5,000 manganese sulphate.
3. 1/10,000 „ „
4. 1/25,000 „ „
5. 1/50,000 „ „
6. 1/100,000 „ „
7. 1/250,000 „ „
8. 1/500,000 „ „
9. 1/1,000,000 „ „ ]
(_b_) _Stimulation in soil cultures._
Roxas carried out pot experiments with rice in soil to which was added
varying proportions of manganese sulphate, with and without the addition
of nutrient salts of ammonium, potassium, and calcium. The criterion
of stimulation was the length of the growing leaves as measured daily,
a strength of M/1000 MnSO₄ (M = molecular weight) giving a favourable
result.
In the Hills Experiments (1903) an increase of produce was obtained
with wheat by manuring with manganese phosphate, chloride, sulphate, or
oxide (MnO₂), while an increase of straw was gained with nitrate, though
this compound decreased the yield of corn. With barley no evidence of
stimulation is set forth for any compound, except that the root growth
was improved by the addition of manganese iodide, in spite of the general
unfavourable action this substance exerted upon germination and growth.
Bertrand (1905) whose work will later be considered in detail,
experimented on arable land, adding quantities of manganese sulphate (?)
equivalent to about 1·6 gm. Mn to each square metre, growing oats from
February to May. Increase of weight was found in the plants growing on
the manganese plots, the differences in favour of manganese being
For total crops 22·5%.
„ grain only 17·4%.
„ straw only 26·0%.
A certain alteration in the quality of the grain was also noted from
the manganese plots, the weight per hectolitre exceeding that from the
untreated plot, the % of water and of total nitrogen being somewhat lower
than that from the untreated, while the ash and the quantity of manganese
present was the same in the grain from both plots. Bertrand suggested
that these results might indicate a new line to follow in the study of
the causes of the soil fertility.
Strampelli (1907) tested the effect of manganese dioxide, carbonate,
and sulphate, and of a manganiferous mineral from the Argentine upon
wheat, and found that while all four substances exercised a favourable
influence on the vegetation, the best result was obtained with the
sulphate. When however other manures were used in conjunction with the
manganese compounds the balance of improvement shifted. With nitrogen,
applied as nitrate of soda, manganese dioxide proved the most beneficial,
with farmyard manure the manganiferous mineral[14], and with blood the
carbonate. It was also found that a manganese compost did not increase
production when phosphatic manure was applied as basic slag.
[14] As no analysis of the mineral is given it is obviously
impossible to say to what constituent the increase is due in this
case.
Feilitzen (1907) indicated that the nature of the soil plays its part in
determining whether manganese acts as a stimulant or not. His experiments
were made in the field on poor moor soil, which carried a little Sphagnum
turf and Eriophorum, and which was poor in food salts. The soil was
prepared and manured and then the plots were watered with a solution of ·1
gm. MnSO₄.4H₂O per litre at the rate of 10 kgm. sulphate per hectare, six
control plots being left untreated. Oats were sown and the soil rolled.
During growth no difference was noted between the various plots, and after
harvesting the weights of the different crops showed that the manganese
had not caused increase of crop in either grain or straw on this poor moor
soil.
The great bulk of the work on this problem has been carried out by various
Japanese investigators, whose work extends over several years. Loew and
Sawa (1902) found that small quantities of manganese sulphate in soil
cultures stimulated the growth of rice, pea, and cabbage. They suggested
that soils of great natural fertility contain manganese in an easily
absorbed condition, and that this forms one of the characteristics of such
soils.
Nagaoka (1903) dealt with plots in the rice fields which had not been
manured for the three previous years and which were then treated with
manure at the rate of 100 kgm. ammonium sulphate, 100 kgm. potassium
carbonate and 100 kgm. double superphosphate per hectare. Twelve series
were worked in triplicate and received manganese sulphate in varying
quantities, equivalent to 0–55 kgm. Mn₂O₃ per hectare, one set of three
being left untreated. The cultivation was normal and the application of
manganese was found to influence the yield of rice. 25 kgm. per hectare
gave the best result and increased the harvest of grains by one-third;
higher doses of Mn₂O₃ gave no better crop. The percentage of grain
relative to the straw was also increased. The increase in both respects
was evident all through the series from 10 to 55 kgm. Mn₂O₃ per hectare.
The conclusion was reached that the application of this salt to soils poor
in manganese would be a commercial advantage.
The next year (1904) the experiments were extended to observe the after
effects of the initial doses of manganese sulphate. The harvest of grain
was greatest in those plots that had received 30 kgm. Mn₂O₃ per hectare,
while it was approached very closely by that from the plot with 25 kgm.
Mn₂O₃, which had proved the best in the first year’s experiments. The
maximum increase of yield over the unmanured plots in the first year was
37%, while in the second year it dropped to 16·9%.
Asō (1904) also obtained an increase of one-third in produce of grain when
25 kgm. Mn₃O₄ per hectare (as manganous chloride) was applied to rice.
The development of the plants was improved and the treated plants flowered
about four days before the untreated ones.
Loew and Honda (1904) grew _Cryptomeria japonica_ in beds, treating the
soil with various manures and with iron or manganese sulphate. The latter
favoured increase in height, and within 1½ years the cubic content of the
trees had increased to double.
Fukutome (1904) grew flax in pot cultures, each pot containing 8 kgm.
soil, to which was added ·4 gm. MnCl₂.4H₂O and ·4 gm. FeSO₄.7H₂O. This
mixture had a marked effect on the growth of the flax, but the individual
salts in doses of ·4 gm. per 8 kgm. soil had but little effect.
Namba (1908) applied manganese salts to onion plants in pots with a
considerable measure of success. Pots containing 8 kgm. loamy soil were
manured and received:
(1) no manganese,
(2) ·1 gm. MnSO₄.4H₂O,
(3) ·2 gm. MnSO₄.4H₂O,
the manganese sulphate being applied in high dilution as top dressing. The
bulbs and leaves were considerably stimulated by small doses of manganese
sulphate, the best results being obtained from (2), which represents a
manuring of 22 kgm. MnSO₄ per hectare. An increase of the dose lessens
the beneficial effect, as the toxic action begins to come into play. The
actual figures obtained may prove of interest.
Wt. leaves Wt. bulbs Total weight Bulbs & roots
& roots Absolute Relative _____________
leaves
gm. gm. gm. gm.
1. 29·5 8·5 38·0 100·0 ·28
2. 38·0 22·5 60·5 159·2 ·59
3. 35·5 16·5 51·0 134·2 ·46
Uchiyama (1907) carried on a variety of experiments with manganese
sulphate on several plants on different soils, both in the field and in
pots, and found that the compound exercised a favourable action in most
cases when applied in appropriate quantities. In summarising his results
he stated that both manganese and iron stimulate the development of
plants, different plants varying in their susceptibility to the action.
Sometimes a joint application of the two salts is the most beneficial,
sometimes an individual application is the better, in which case manganese
sulphate is generally better than ferric sulphate in its action. The
stimulating action of manganese varies greatly with the character of the
soil, and the mode of application also affects results. As a general rule
the manganese acts best when applied as a top dressing rather than when
added together with the manure. Further the stimulating action differs
greatly with the nature and reaction of the manurial mixture. Uchiyama
concludes that 20–50 kgm. per hectare of crystallised manganese sulphate
is a good general amount to apply.
Takeuchi (1909) corroborates the statements of the various writers that
plants differ in their response to the manganese manuring. Pot cultures,
in each of which 8 kgm. soil were similarly manured, received ·2 gm.
MnSO₄.4H₂O applied as a solution of 1/100 strength, the controls receiving
the same amount of water. The manganese increased the green weight of
spinach by 41%, while the dry weight of barley, peas and flax rose 5·3%,
19·4%, and 13·9% respectively above that of the untreated. The control
plants of flax were behind the manganese plants in growth and flowering,
while barley was the least stimulated of all the test-plants. Other
observations seemed to show that Leguminosae and Cruciferae are more
susceptible to manganese stimulation than are the Gramineae.
III. EFFECT OF MANGANESE COMPOUNDS ON CERTAIN OF THE LOWER PLANTS.
The information on this point is exceedingly meagre, possibly because of
the diversion of general attention to the higher plants in view of the
commercial interests involved.
Richards (1897) carried out experiments with various nutritive media
with the addition of certain metallic salts, including those of zinc,
iron, aluminium and manganese. The fungi tested were _Aspergillus niger_,
_Penicillium glaucum_ and _Botrytis cinerea_. His general conclusion was
that fungi may be stimulated, though it must not be concluded without
further investigation that all fungi react in the same degree to the same
reagent, but this conclusion is traversed by Loew and Sawa (1902). These
writers state that fungi are _not_ stimulated by manganese, and take this
as a proof that the improvement in the growth of phanerogams, induced by
manganese compounds, is not due to direct stimulation of the protoplasmic
activity, but to some other more obscure cause.
IV. PHYSIOLOGICAL CONSIDERATIONS OF MANGANESE STIMULATION.
The physiological cause of the stimulation exerted by manganese compounds
has raised much controversy. Loew and Sawa suggested that the action of
the sun’s rays upon a normal plant puts a certain check on growth, arising
out of the action of certain noxious compounds which they supposed to be
produced in the cells under the influence of light. The stimulation of the
manganese compounds may be due to a supposed increase in the oxidising
powers of the oxidising enzymes, so that destruction of the checking
compounds can be accomplished as quickly as they are formed, so enabling
growth to continue more rapidly.
Asō (1902) had previously stated that colorimetric tests for oxidising
enzymes indicate that the yellowish leaves from plants treated with
manganese compounds give reactions of higher intensity than the green
leaves from control plants, the difference between the reactions being
specially marked in barley, and less so in radish.
Bertrand has devoted much time to the consideration of this and allied
problems. In 1897 (a, b, c) he proceeded to investigate the essential
nature of manganese in the economy of the plant, his experiments showing
its constant presence in a ferment (laccase) obtained from plants. He
also extracted from lucerne a substance very poor in manganese, which
was somewhat inactive, but which regained or increased its activity on
the addition of manganese. Bertrand stated that manganese was apparently
not to be replaced by another metal, not even by iron, and that the small
quantity of it occurring was no reason for regarding it as a _secondary_
element in the composition of plants. The view was also put forward that
in the presence of certain organic substances, such as hydroquinone,
pyrogallol or similar bodies, manganese is capable of fixing free oxygen
from the air, the volume of oxygen absorbed varying according to the
compound of manganese used. Bertrand was led to conceive the oxydases
as special combinations of manganese in which the acid radicle, probably
protein in nature and variable according to the ferment considered, would
have just the necessary affinity to maintain the metal in solution, i.e.
the form the most suitable for the part it has to play. The manganese
would then be, according to his view, the true active element of oxydase,
which functions as the “activator”; the albuminous matter, on the other
hand, gives to the ferment those special characters, which show themselves
in their behaviour with regard to reagents and physical agents. From this
point of view manganese could no longer be considered as a non-essential
element, but as a substance of vital necessity to the functions of
plant-life. The name “complementary” manure was suggested for compounds of
such elements as manganese, which exert a physiological action and which
were proposed for use as manures. Later (1905) Bertrand considered that
he had still further proved the indispensable nature of manganese. The
absence or insufficiency of one essential element arrests or diminishes
growth. This applies not only to those substances which are present in the
greatest abundance, such as C, P, N, &c., but also to those elements like
manganese, boron, and iodine, which only occur in traces. These elements
are usually specialised in function, and for them the name “catalytic”
elements was suggested, in view of the work they are held to do. As late
as 1910 the rôle of manganese in the functioning of the oxidising enzymes
was again insisted on. It was concluded that manganese intervenes as a
catalytic agent in the material changes of which plants are the seat,
and that it participates in an indirect manner in the building up of the
tissues and in the production of organic matter.
_Conclusion._
Manganese exerts a toxic influence upon the higher plants, if it is
presented in high concentration, but, in the absence of great excess
of the manganese compounds, the poisoning effect is overshadowed by a
definite stimulation. As is the case with boron, manganese stimulates some
species more than others, the action on barley being more evident than
that on peas. It seems probable that manganese may prove to be an element
essential to the economy of plant life, even though the quantity usually
found in plants is very small.