GERMINATION.

We have ascertained that a seed, considered with reference to its organization, consists, 1st. of an embryo which includes the germs of the root and of the stem; and 2d. of the cotyledon, or cotyledons. Considered with reference to their chemical compositions, seeds exhibit a certain similarity of constitution. They contain: 1st. starch and gum; 2d. a highly azotized matter analogous to the caseum of milk and animal albumen; this is the matter which is commonly and very improperly designated under the name of gluten, and of vegetable albumen; 3d. a fatty or oily matter, rich in carbon and hydrogen. Seeds contain either fixed oils, such as hemp-seed, rape-seed, &c., or volatile oils, as aniseed, cummin-seed, &c. The different principles which are associated in the seeds vary considerably in their relative proportions: they also vary slightly in their nature. One seed, that of the colewort, for example, will contain more than forty per cent. of its weight of oily matter, while another, such as wheat, will only contain a few hundredths. Oats may contain ten or twelve per cent. of caseum or gluten; in certain varieties of wheat, analysis indicates a much larger quantity. The proportions of starch, gum, sugar, or mucilage do not vary less. It almost always happens that these different substances are found associated in the same seed; sometimes one predominates and the others only enter in very small proportion.

After burning, the ashes of seeds are always found composed of phosphates, sulphates, and alkaline and earthy chlorides. These ashes also contain silica, and certain carbonates produced by the destruction of salts formed by organic acids.

If some seeds, sufficiently moistened, are placed under a bellglass containing atmospheric air confined over quicksilver, all the signs of germination will soon be perceived. In the course of a few days, provided the temperature has been sufficiently high, germination will have made a certain progress. Supposing that the temperature of the bell-glass has not varied, and that the atmospheric pressure remains the same, we generally find that the air, in which germination has been proceeding, has not changed its original volume; but it has been modified in its composition: a notable quantity of carbonic acid has been formed, and a portion of oxygen has disappeared. The volume of carbonic acid produced, represents for the most part the volume of oxygen which has disappeared. Now we know that carbon being burnt in a certain volume of oxygen gas, produces sensibly an equal volume of carbonic acid gas. It was the knowledge of this fact that induced M. de Saussure to say, that in germination, carbonic acid is produced by the combustion of a portion of the carbon which enters into the composition of the seed.

Germination and the appearance of carbonic acid, (which is always its consequence,) take place as readily in pure oxygen gas, as in atmospheric air; but if placed in an atmosphere deprived of oxygen, seeds cease to germinate. Consequently, germination is out of the question in azote, in hydrogen, or in carbonic acid, however fa

vorable they may be in reference to humidity and temperature. Some formation of carbonic acid is indeed to be observed under such circumstances, but then this gas is the result of the decomposition and putrid fermentation of the seed. It is therefore by means of the oxygen which it contains, that atmospheric air concurs in the germination of seeds.

Rollo was the first who ascertained the production of carbonic acid, during the germination of seeds in an atmosphere of oxygen; but it was M. Theodore de Saussure, who by delicate eudiometrical experiments, demonstrated the phenomena in all their nicety, by proving that the oxygen consumed was replaced by a corresponding volume of carbonic acid.*

There are some seeds, for instance, peas, and the seeds of aquatic plants, which have the property of germinating under water. Some observers have, from this fact, come to the premature conclusion that atmospheric air, and consequently oxygen, were by no means necessary to germination. Saussure has explained this anomaly by referring to the constant presence of air in a state of solution in water. In fact, having placed some seeds of the polygonum amphibium under water, deprived of its air by long boiling, Saussure proved that germination could not take place.†

Under like circumstances, the quantity of carbonic acid generated in a given time, is by so much greater, the larger the quantity of oxygen in the atmosphere which immediately surrounds the germinating seed. Carbonic acid gas is, of all the gases which have been tried, that which is most unfavorable to germination; and one way of hastening the process is to place under the receivers which cover the seed, some substance capable of absorbing it as fast as it is formed-quick-lime, for example. By this arrangement the radicular increase is sensibly accelerated.‡

The quantity of oxygen gas necessary to germination, is not the same in reference to all seeds; lettuce, the french-bean, and the field-bean require aboutth part of their respective weights; while

10

th less is sufficient for wheat, barley, purslane, &c. Saussure moreover came to the conclusion that the carbonic acid generated by these different seeds in germinating is proportioned to their mass, and altogether independent of their number.§

Inasmuch as seeds during germination yield carbonic acid to the atmosphere, it is quite obvious that they must lose some part of their original weight. And this they do in fact; but the loss experienced by seeds which have germinated is always greater than that which would have resulted from the destruction of carbon that takes place. Saussure attributed this excess of loss to the volatilization of a portion of the water which entered into the composition of the seed. According to Saussure, therefore, the phenomena of germination resolve themselves into the diminution of carbon and of the elements of water. It is, nevertheless, doubtful whether the chemical actions

* Saussure, Recherches chimiques sur la Végétation, p. 10.
t Idem, p. 3. ‡ Idem, p. 26.
Idem, p. 13.

|| Idem, p. 20.

are so simple as this; we know, for example, that M. Becquerel considered the organic acid which appears during germination as acetic acid, whereas it is much more likely that it should be the lactic acid. There is certainty of the formation of an acid during germination; to prove its development it is sufficient to make a few moist seeds sprout on blue litmus paper, which speedily acquires the permanent red tint indicating the presence of an acid.

The volume of the air in which seeds germinate is not absolutely invariable. On examining, with renewed attention, the action of germinating seeds on a limited volume of air, M. de Saussure ascertained that certain seeds have the property of diminishing the bulk of this atmosphere, while others perceptibly augment it. It must be admitted, therefore, that during germination, the volume of carbonic acid produced is now greater, now less, than the volume of oxygen gas that is consumed. The nature of the results obtained appears, however, to vary in regard to the same class according to the stage of the germination.

Elementary analysis appeared to me the most satisfactory means of investigating the subject of germination. I shall here recapitulate a few attempts that have been made in this direction, less however with a view to the final settlement of the question, than to point out the general method of procedure to those who would enter farther upon this interesting portion of physiology. The experiments I allude to were made upon the seed of trefoil and on wheat.

The seed, on being dried at a heat of 110° cent. (230° Fahr.,) lost 0.120 of water. Duly moistened, it was placed to sprout on a porcelain plate. As soon as the radicle had attained a length of from 1 th to th of an inch, each seed was placed in a stove, the temerature of which was sufficiently high to check the growth immediately. The complete desiccation was then terminated over an oil bath at a temperature of 110° cent. (230° Fahr.)

40

20

The seed put to germinate weighed 2.474 grammes, (38.193 grains troy ;) perfectly dry, its weight would have been 2.405 grms. (37.128 grains troy.) When germinated, the seed, also quite dry, weighed 2.241 grms. (34.596 grains troy.)

Analysis gives us the composition of

The total loss then during germination was 0.164 grm., (2.531 grs.) while the loss due to the carbon, only amounts to 0.068 grm. (1.049

grs.:) the analysis shows besides that in this particular case, the excess of the loss in the present case over and above that which is ascribed to the carbon, is not altogether due to the elements of water, inasmuch as it is partly ascribable to carbonic oxide: for

1.049 grs. of carbon,

66
1.404 of oxygen,

Represent 2.453 " of oxide of carbon.

Supposing this to be so, and the first period of the germination of the trefoil to have been conducted in a close vessel, the volume of atmospheric air would have been increased; because 1 volume of carbonic oxide+volume of oxygen-1 volume of carbonic acid gas. It is consequently evident that for each volume of carbonic oxide produced from the seed, there is one half of this volume added to the total volume of the atmosphere.

It will not, perhaps, be useless to advert to the circumstance that the increase of volume, which in the experiment I have just related must have amounted to about twenty-five cubic inches, would certainly have passed undetected, if the experiment had been conducted in a close vessel. For inasmuch as several quarts of atmospheric air must have been used to place 38.193 grs. of seed in conditions favorable for germination, it may readily be imagined that the increase of volume must have been too small a fraction of the total mass of air to be appreciated with any certainty.

GERMINATION OF WHEAT.

The wheat employed, on being dried, lost 0.652 grain of moisture. Thirty-one grains were arranged for germination, which process was suspended immediately after the appearance of the radicles. The young stalks were hardly visible. The germinated grain looked slightly shrivelled on being crushed, after having been dried, it scarcely differed in appearance from ordinary wheat reduced to powder, a considerable quantity of starch being still recognisable. The wheat, before germinating, taken as dry, and free from ashes, weighed 2.439 grms., or 37.653 grs. troy.

The seed when germinated and gathered, under the same condition, weighed 2.365 grms., or 36.510 grs. troy.

Elementary analysis gives for the composition of—

*

0.324 of a grain of carbon +0.432 of a grain of oxygen represent 0.756 of a grain of carbonic oxide; 0.030 of a grain of hydrogen would require 0.247 of a grain of oxygen to form water. Now, the oxygen remaining, abstraction made of that which enters into the formation of the carbonic oxide is 0.282 of a grain.

In the first period of its germination, therefore wheat, like trefoil seed, experiences a loss which may in great part be referred to elimination of the carbonic oxide. The chemical composition of these two kinds of seed at more advanced periods of their germination, no longer presents relations so simple. We easily discover that carbon continues to be eliminated; but the loss no longer corresponds with that which the oxygen of the seed ought to suffer, in order that the total loss should be represented by a definite compound of carbon. The phenomenon, in fact, becomes extremely complex; and we can even perceive that it must be so, when we reflect that in proportion as the green parts are evolved, a new chemical action is set up entirely different from that which takes place in the earliest periods of the germination: the green matter of vegetables having, as we shall find, the singular faculty of decomposing carbonic acid gas, and assimilating its carbon under the agency of light.

This action of the green matter begins to be manifested long before the first phases of germination have entirely ceased; so that during a certain time two opposite forces are at work simultaneously. One of these, as we have seen, tends to discharge carbon from the seed; the other tends to accumulate this element within it. So long as the first of these forces predominates, the seed loses carbon; but with the appearance of the green matter the young plant recovers a portion of this principle; finally, when by the progress of the vegetation, the second force surpasses the first in energy, the plant grows, increases, and advances to maturity.

The presence of light is indispensable to the manifestation of the chemical force by which the green parts of plants appropriate the gaseous elements of the atmosphere. Germination, on the contrary, may take place in absolute darkness; and it would be curious to inquire into the issues of vegetation begun and ended under such circumstances, in which the organs produced by the seed would have no power to fix any of the principles of the atmosphere to repair the loss of carbon which the seed suffers. It is evident that this loss of carbon must have a limit, which is probably that of germination.

CONTINUED GERMINATION OF PEAS.

Ten peas, weighing together 2.237 grms. or 34.534 grs. troy, taken as quite dry, were put to germinate in a dusky room, the temperature of which was maintained between 12° and 17° cent. (54° and 63° Fahr.) The experiment, begun the 5th of May, was ended on the 1st of July.

The germinated peas, when dried, weighed 1.075 grm. or 16.595 grs. troy.