88 PROCEEDINGS OF THE ACADEMY OF [1899. 



III. SaNICULA — A BIOLOGICAL STUDY. 



Examiuing a plant of Sanicula Marilandica, a strikiDg point 

 presents itself in its bi'ancliiug character. These branchlets are 

 usually in threes, and exceptionally in fours. That acute observer, 

 Rafinesque, noticed this, and it was doubtless on account of this 

 striking character that he proposed the name of Triclviium, when 

 he thought to make a new genus out of the older Sanicula. 



I have endeavored to teach iu numerous papers, that by far tuo 

 much is claimed for environment in the evolution of form. It 

 would rather seem that form depends on a purely mathematical law 

 of growth-force. Growth is not a continuous operation, but rhyth- 

 mic. The degree of force depends on a supply of nutrition and 

 the ability of the plant cell to avail itself of the supply. As, 

 therefore, each rhythmic wave varies in intensity, the ultimate form 

 of the immediate structure under the influence of that wave must 

 vary accordingly. 



Again I have taught that even sex is influenced by like condi- 

 tions. Those parts of the flower or portions of a plant under the 

 influence of a vigorous growth-wave laden with nutrition favor 

 the production of female organs — the feeble wave is productive of 

 male organs only. 



A study of Sanieula well illustrates these points. The first 

 growth-wave ceases at the first pair of leaves. This must have 

 been very sudden ; for the main axis has been so deprived of food, 

 and its vital power rendered so weak, that it can only make a feeble 

 growth with the advance of the next wave. The consequence is 

 that the growth- wave is turned into the two axillary buds. They 

 take the place of the original axis, and we have two leading 

 branches instead of one. The original axis remains a weak, 

 threadlike, common pedicel, which bears usually but a single fertile 

 flower and numerous barren ones. In some species of jjlants the 

 centi'a] axis utterly fails under the shock of the rhythmic growth. 

 In that case we have the dichotomous mode of branching. 



Passing the eye along the stem, we find the growth- wave, rhyth- 

 mic as it is, decreasing in vigor. The central axis profits more 

 by nutrition — the branches from the axial buds are less like leaders 

 — and by the time the terminal point is reached Ave find it sur- 

 mounted by a fruit on a pedicel much stronger than the lateral ones. 



