DARWIN MEMORIAL. 85 



here to commemorate to have demonstrated this truth to the entire 

 satisfaction of the united scientific world. 



Darwin has actually solved the great problem of phytology, so 

 long supposed to be incapable of solution, viz : Why does the root 

 grow downward and the stem upward ? Briefly and roughly stated, 

 the answer to this question is that, as the bursting seed pushes out 

 its two germinal points these circumnutate from the first, and thus 

 explore their surroundings for the means of benefiting the plant. 

 To employ Darwin's own word, they ''perceive" the advantage 

 that would result from the penetration of the soil, on the one 

 hand, and from the ascent into the free air and sunlight, on the 

 other, and through the pre-Darwinian law of the " physiological 

 division of labor," the one hQcova&s gcotropic and the other heliotropic 

 — the one develops into a radicle and then into a root, while the 

 other develops into an epicotyl and then into a stem. 



I will only add to the thoughts already presented that Darwin's 

 discovery of the existence in all plants of an innate and spontaneous 

 mobility belonging to them as forms of organic life, possesses an 

 important ulterior significance. 



The law of natural selection, as a fundamental process, has long 

 since passed the stage of discussion. But there has always remained 

 one unsettled question lying at its very base which Darwin him- 

 self admitted to be an open one. That question concerns the 

 cause itself of variation. It is granted that, admitting the tendency 

 to vary, all the results claimed for natural selection must follow; but 

 many declare that, in this very tendency to vary, there is a mystery 

 as great as the mystery of life itself. 



It is only in this work on the " Power of Movement in Plants" 

 that Darwin has really assailed this last fortress of supernaturalism. 

 Not that he has avowed any such purpose, for of this he would have 

 been incapable, but so skilfully and so powerfully has he marshaled 

 the facts that the conclusion follows without being stated. No one 

 can doubt that he perceived this, and I, for one, am convinced 

 that he saw it from afar, and that it was the great end of his labors; 



