47 



lish thorn hero in order to explain to observers the defects of an 

 experimental process to which, in the futnre, they wonld themselves 

 have been tempted to resort : this, moreover, seems to me the more 

 iisefnl in that np to this time this danger does not seem to have struck 

 the attention of botanists. On the other hand, my observations con- 

 lain some new data relative to the temperatures favorable for the 

 L'ormination 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 dift'erence 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 draAvs 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 accelerat- 

 ing influence upon the absorption of oxygen by seeds in the i)rocess of 

 germination. All the experiments made in a strong light have not, 

 liowever. 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 shoAved 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. S 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 Xos. 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 relatirm between the degree of light and the 

 ((uantity of oxygen absorljed. Thus, in a diffuse light this accelerat- 

 ing influence shows itself in a most marked manner when the sky 

 is very clear, and the solar radiation reaches us in its greatest inten- 

 sity. Such was the case in exix'riments Nos. 2 and 8. Whenever the 

 sky is cloudy this action is more and more weakened and ceases 

 altogether when the sun is coni])letely veiled, as in stormy weather, 

 so that there is a semiobscurity. 



