Researches in Vegetahle Physiology, 143 



may appear more ungrateful, that tlie scientific men of tlie pre- 

 sent day will succeed in perfecting the work which lias been 

 commenced, and introduce into the sketch which has been 

 handed down to us the finish of a perfect picture. 



These general reflections, which I believe to be true for all 

 the sciences, apply particularly Avell to vegetable physiology. 



The principal features of the life of plants are known to us ; 

 and Ave can nearly follow the different phases of development 

 from the first vital movements of the germinating seed to the 

 moment Avhen the products of vegetation are accumulating in 

 the fruit and thus preparing a new generation. 



But if the general outlines are known, how many details 

 are still wanting ! how many phenomena which escape us, at 

 all events in part ! how many questions to be solved ! 



The number of those who devote themselves to this task is 

 great ; and if Ave wish to give a sketch of the present state of 

 science, we are only embarrassed to choose in the midst ©f the 

 materials which present themselves on all hands. All nations 

 assist in the work, but none so much as the Germans. Since 

 the time of De CandoUe vegetable physiology has shoAvn a 

 tendency to natui*alize itself in Germany ; and although Ave 

 can cite among the naturalists belonging to other nations many 

 names Avhich are advantageously known to us, it is nevertheless 

 to the Germans that Ave must give the honour of most of the 

 very modern discoveries, and of those which have most con- 

 tributed to give the science its present form and tendencies. 



Whilst the works are numerous, their very form renders 

 them difficult to analyse ; many may be said to be only ac- 

 counts of extremely minute experiments Avhich it is impossible 

 to depict in broad lines. We must not expect to find in them 

 striking results of a kind to open up ncAv horizons. Some 

 only confirm already -known facts ; others introduce slight mo- 

 difications of these Avithout changing their general character. 



I. 



At the base of physiological researches we shall always find 

 those Avhich treat of the relation of the plant and of light, and 

 particularly of the interesting and varied part played by chlo- 

 rophyl in vegetable life. 



Professor Sachs was the first to indicate the curious and un- 

 expected phenomenon of a diminution in the intensity of the 

 colour of chlorophyl under the direct influence of the sun's 

 rays*. In other words, if a portion of the leaves is sheltered 

 by a screen of some kind, it soon contrasts by its darker colour 

 with the other parts, Avhich are exposed to the sun. 



* Physiologie veg^tale, trad. Fran9. p. 16. 



