Physiology of Plants. 77 



(d) Growth and Development. The questions which 

 interested Sachs most keenly were concerned with the 

 conditions of growth and development ("physiological 

 morphology "), and he approached these in three ways, 

 (i) in his researches on the influence of the environ- 

 ment, e.g. light, he studied some of the normal stimuli 

 to which plant protoplasm reacts. Thus, to take a 

 relatively simple case, he showed that the formation of 

 blossoms depends directly or indirectly upon light and 

 particular rays of light, for it is only by the assimilatory 

 activity of the leaves in light that the particular ma- 

 terials required to produce flowers can be produced; 

 and the development of the flowers is suppressed in 

 plants grown in light which has lost its ultra-violet rays 

 by passing through a solution of quinine. His investi- 

 gation of reactions to gravity, moisture, &c., have also 

 a bearing upon the same problem. (2) He was first to 

 throw a clear light on the relations between growth and 

 cell-arrangement, maintaining firmly that the former 

 determines the latter, and not vice versa. He also for- 

 mulated two general laws of cell-division. (3) He held 

 a particular theory of specific organ-forming substances, 

 which find their way to their proper areas within the 

 growing plant. This theory will doubtless be developed 

 in a work (which he left in manuscript) entitled " Prin- 

 cipien Vegetabilischer Gestaltung" (Principles of Vege- 

 table Form). As far as we understand, in his evolu- 

 tionary views he agreed with Nageli rather than with 

 Darwin. 



In the higher animals some of the facts of sex and 

 reproduction are very conspicuous, and could never be 

 hidden from the observer, though they might Reproduction 

 be, and often were, misunderstood. Man's in Plants. 

 own zoological position as a mammal gave him a clue. 

 In plants, however, even the elementary facts of sex 

 and reproduction eluded detection for many centuries. 

 Not that they are in any way concealed, in the higher 

 plants (Phanerogams) at least, for there is no more 

 flaunting sexuality than that of the lily; it was simply 

 that, in its superficial expression, the sexual reproduc- 

 tion of plants is very different from that in animals. 



