lish them here in order to explain to observers the defects of an experimental process to which, in the future, they would themselves have been tempted to resort; this, moreover, seems to me the more useful in that up to this time this danger does not seem to have struck the attention of botanists. On the other hand, my observations contain some new data relative to the temperatures favorable for the germination of certain exotic seeds.

In consequence of the conclusions to which we have thus been led, it would be useless to study the action of the different portions of the solar spectrum on the apparent progress of germination. How, in fact, can we suppose, in view of the contradictory results already obtained for the condition of light and of darkness-that is to say, for the most extreme conditions--that the employment of the same method can reveal a difference of action for the various portions of the spectrum?

Is it then necessary, after this first fruitless attempt, to give up the solution of the problem, or shall we seek it by another and better method? It is this latter alternative that I have adopted in that I have taken for the basis of a new series of observtions the variations. of a physiological process that, in an almost mathematical manner, measures the germinal activity of the vegetable embryo, namely, the respiration.

After giving the details of his experiments on respiration of plants, Pauchon draws the following conclusions (p. 166):

The laws brought prominently forward by the results of these experiments are:

(1) Light exercises a constant and more or less marked accelerating influence upon the absorption of oxygen by seeds in the process of germination. All the experiments made in a strong light have not, however, the same value in demonstrating this fact. But if we have doubts about the precision of the results furnished by experiments in which germination did not invariably take place (and we believe that we have shown by some preparatory experiments that these results have at least a relative value), this certainly is not the case with experiments Nos. 2 and 8, in which all the seeds did germinate. Thus experiment No. 2 showed in favor of light a result as to the oxygen absorbed twice as great as that given by the seeds placed in the dark. In the same way in experiment No. 8 this superiority reaches to one-third of the quantity of oxygen absorbed by the seeds placed in the dark. Finally, the other experiments, and particularly those classed under Nos. 3, 6, and 7, further confirm the generality of this action of light, which we will, besides, find again in a second series of experiments reported hereafter, several of which have shown unanimity of germination in both cases.

(2) There exists a relation between the degree of light and the quantity of oxygen absorbed. Thus, in a diffuse light this accelerating influence shows itself in a most marked manner when the sky is very clear, and the solar radiation reaches us in its greatest intensity. Such was the case in experiments Nos. 2 and 8. Whenever the sky is cloudy this action is more and more weakened and ceases altogether when the sun is completely veiled, as in stormy weather, so that there is a semiobscurity.

However, in all the experiments where the final result has been favorable to the action of light I have convinced myself that a cloudy sky for twelve hours always showed itself in the amount of the absorption of oxygen in such a manner that the examination of these figures, noted day by day, would almost serve to show the state of the atmosphere during the day which preceded the observation. A very conclusive instance of this action is given us by experiment No. 4 of the second series, in which the state of the sky being carefully observed it showed very marked changes.

(3) The accelerating influence exercised upon seeds exposed to the action of light during the day did not stop at night; it continued to act in the dark with an equal, sometimes even with a greater intensity. I will cite as examples experiments Nos. 3, 4, 6, 7, and 8, when observations made twice a day, morning and evening, allowed of examining the fact I state. How can we explain this persistent action of light? One hypothesis only can be admitted. A portion of the action of the light absorbed by the grain during the day is stored up by it and used by it at night to accelerate its respiration. The proof of this is that the differences of elevation [or quantities of absorbed oxygen] shown in the morning by the instruments for seeds kept in the dark are always below those shown by the instruments and plants in the light. The influence of the light, then, continues for a certain time, at least several hours, even after the light itself has ceased to act; on the other hand, however, this action is not exerted immediately. There is one other phenomenon that we have demonstrated by our experiments. Suppose the sky to be very clear; the differences in favor of light are only apparent after two or three days and become much more marked toward the end of the experiment; that is to say, in proportion as the daily action of sunlight is more and more frequently repeated.

(4) I should also call attention to still another peculiarity, viz, that the differences in the quantities of oxygen absorbed in the dark and in the light were generally much greater at the beginning of these researches than in the later experiments, and particularly in those of the second series. The temperature appears to me to be the only element that varied in these experiments. There must therefore be a more intense respiratory action exercised by light at low temperatures, and this influence would become weakened at high temperatures. This fact would be in entire agreement with the demands of physiology. It is easy of comprehension that a scarcity of heat should be counterbalanced by the action of light, which furnishes for the reaction of the respiratory organs the force that they could not obtain from an insufficient temperature. On the contrary, when the heat is intense the intervention of the light is no longer necessary, the first cause being sufficient to excite the process of germination in the protoplasm of the seeds.

(5) This action of light seems to differ a little according as it acts upon seeds containing albumen or those without albumen. In the case of the albuminous seeds of the castor-oil plant the advantage was much more apparent in favor of those exposed to the light, which advantage appeared to me much less decided for the seeds without albumen, such as the haricot bean. Nevertheless, as the experiments were not invariable in their results, the cause of the variations ob

served can also be accounted for by attributing them to certain differences in the atmospheric conditions.

(6) The more considerable absorption of oxygen by seeds under the influence of light explains the fact that asparagine (the medium for the conveyance of the reserved albuminous substances in the germination of leguminous plants) only disappears in plants exposed to the light and continues present in those raised in the dark. The comparative researches of Pfeffer (1872) upon the chemical composition of asparagine and other substances showed that asparagine is poorer in carbon and in hydrogen and richer in oxygen than legumine and other albuminoids. The transformation of legumine into asparagine is accompanied by the absorption of a certain quantity of oxygen. On the other hand, it is effected only by the influence of light, the reason being that light increases the quantity of oxygen absorbed, and therefore exerts only an indirect influence on this change, as had already been surmised even when we were not acquainted with the reasons.

(7) Other new and important conclusions become apparent from these experiments and those which follow, and although they have no direct connection with the subject of my work I think it will be well to designate them briefly.

The quantity of oxygen absorbed in a certain space of time by a seed in process of germination varies very considerably according to the temperature; it increases with it, as has been already proved in treating of the respiration of plants in the dark. The general results of my experiments, and particularly of Nos. 9 and 10, leave no doubt of this fact. We can therefore easily understand what errors have been committed by those experimentalists who have given calculations of this absorption of oxygen by certain seeds without taking into consideration the conditions as to temperature. Their figures have no value whatever, particularly in view of a fact stated by me several times already, viz, that the quantity of oxygen absorbed by a seed is not at all in proportion to its apparent development, but, on the contrary, undergoes considerable variation, depending upon the influence of the external agents affecting the phenomenon. According to my observations, this quantity may vary as two to one, or even more, in two plants of identically the same weight, but placed in different thermic conditions from the commencement of their germination to the emerging of the rootlet. From this point of view, then, the plant acts like a complete organism, its respiratory action being accelerated or retarded always, however, within physiological limits, like those of an animal under the influence of certain exterior changes.

Having thus shown that germinating seeds absorb more oxygen in the light than in darkness, Pauchon conducted some experiments to determine the ratio between the oxygen and the carbonic acid, and draws the following conclusions (see page 182 of his work):

Experiments Nos. 3 and 4 have a real value for the solution of the problem brought forward in this part of my work. As to the partial results given by experiments Nos. 1, 2, and 5, their accuracy can not be doubted; therefore I shall make use of them as confirmatory docuI must repeat that the numbers used for the proportions of 2667-05 M- 4

carbonic acid are a little smaller than they should be in reality, in consequence of peculiarities inherent to the method and already explained; but as this diminution, which is almost insignificant, is equally present in all the quantities, the result is that the numerical quantities are always comparable, although the ratio may be diminished in an inappreciable degree. Finally, I may add that the conclusions which follow are only applicable to plants under precisely the same conditions as those under which my experiments were conducted.

(1) I note, first, that experiments Nos. 3 and 4 confirm in the most precise manner the general fact of the accelerating influence exercised by light upon the absorption of oxygen; but, these experiments having been carried out at a higher mean temperature, the differences in the quantity of oxygen absorbed in the light and in the dark are generally less than in the first series of experiments.

(2) As to the exact relative quantities of carbonic acid exhaled, it was a little more for the castor-oil plant in the dark than in the light, the contrary being the case for the scarlet runner bean. From this we might conclude that the influence of light produces doubly favorable effects upon the germination of the castor-oil plant, (a) by increasing the absorption of oxygen and (b) by diminishing the exhalation of carbonic acid, thereby increasing the gain of oxygen by reducing the expenditure of carbon and oxygen. (It must not be forgotten, in this explanation, that one volume of carbonic acid gas contains one volume of oxygen.) From this particular point of view the scarlet runner bean seems to be less favored than the castoroil plant, although the excess of the quantity of carbonic acid exhaled by either placed in the light is nearly insignificant when compared with that exhaled by the same species kept in the dark.

CO

(3) In the dark the ratio divided equally between the seed of the castor-oil plant and those of the haricot bean, was at least a third more in favor of the latter than the ratio obtained for the castor-oil plant. The length of the experiment appears to me to have exercised a certain influence upon this ratio. Thus, for the castor-oil plant the figures reached 0.586 in experiment No. 2, which lasted about four days, and 0.771 in experiment No. 3, which lasted five days. The same was the case with the haricot bean; the result was 1.138 for experiment No. 4, which terminated during the fourth day, and 1.034 for experiment No. 5, which was prolonged until the sixth day. In a word, the prolongation of the experiment

as determined by four experiments

CO2 (

tends to render the ratio equal to unity. With the duration of

the experiment this ratio rises in those cases where it is below 1, but diminishes where it is above 1, until the seed is consumed and the period of vegetation, properly so called, arrives, during which latter time the final limit may be reached when the quantities of oxygen absorbed and the carbonic acid exhaled balance perfectly.

(4) In the light the ratio

CO2
Ο

is about a third more for the

haricot bean than for the castor-oil plant. But the sum obtained in experiment No. 2 was very much below that stated in experiment No. 5. The duration of this experiment and its prolongation until the approach of the vegetating period appears to me to account for this difference. This hypothesis is supported by the results of experiments Nos. 1 and 4, the first having lasted six days and the other less than four.

(5) By comparing the ratio CO2 for similar experiments made in

the light and in the dark, we see that there is always a difference of a quarter of the value of this ratio in favor of the dark; or, in other words, a seed placed in the dark always exhales more carbonic acid for the same quantity of oxygen absorbed than a seed kept in the light, even although sometimes, as we showed in experiment No. 3, the absolute quantity of carbonic acid exhaled is less in the light than it is in the dark. Finally, while in the light the carbonic acid released is always much less in quantity than the oxygen absorbed, the contrary may be the case in the dark, where the absolute amount of carbonic acid may even exceed the absolute quantity of oxygen, as is proved in experiment No. 4, where the absorption of oxygen 37.36 corresponds to an exhalation of 42.54 of carbonic acid.

(6) In order to consider the influence exerted upon the ratio CO2 b

by

the nature of the grain itself under different conditions as to light and darkness, it is only necessary to consult the conclusions which precede, and note the marked differences that distinguish the albuminous and oily seed of the castor oil from the nonalbuminous and starchy haricot bean.

(7) The facts which precede complete the explanation already given of the transformation of legumin into asparagin under the influence of light. In general, the absorption of a greater quantity of oxygen only assures the formation of asparagin in so far as the amount of carbonic acid exhaled is less than the amount of oxygen absorbed; since asparagin is poorer in carbonic acid and richer in oxygen than legumin, all the conditions favorable to that formation are to be found demonstrated in the results of experiment No. 4, with seeds exposed to the light. It is very probable that a portion of the oxygen which had disappeared and that was not found as carbonic acid was absorbed by the albuminoids when forming asparagin, and we know from other sources that this substance seems to form in the majority of seeds during the process of germination.

This absorption of oxygen during the period of germination is still greater in the castor-oil seed than in that of the bean. The oily seed, therefore, seems to be more favored by nature from a physiological point of view.

(8) We might be tempted to compare the ratio

CO2
O

obtained during

the time of germination, with the same ratio during the period of vegetation. But the sum for the vegetating epoch has only been precisely fixed in the dark, which for green plants is entirely an abnormal state. As, on the other hand, it is impossible to gauge exactly