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THE AMERICAN NATURALIST [Vol. XLIII 



main the basis 'of our knowledge of these interesting 

 forms. He pushed it as far as his means at hand per- 

 mitted, and while in many points he could not arrive at 

 definite conclusions, it is a fact that most of his un- 

 answered questions are unanswered still. While his 

 knowledge of plant physiology may not have been broad 

 enough for him to correlate this special form of nutrition, 

 with the general problems of plant metabolism it is to 

 be remembered that after all it was not from such a stand- 

 point that he took up the problem. 



There is one characteristic which is particularly ad- 

 mirable in all of Darwin's botanical work and that was 

 his endeavor in so far as he could to examine an abun- 

 dance of different forms which would illustrate any topic 

 under investigation. This is the more to be remarked 

 since he was not really very fortunately placed in the 

 matter of obtaining material. For keeping his plants 

 after he had obtained them he had to depend entirely 

 upon such facilities as his own garden and greenhouse 

 afforded. Being unable himself to collect material to 

 any extent, he had to depend upon the generosity of his 

 friends and correspondents, who, it may be said, responded 

 with alacrity. None but one of very active mind and great 

 perseverance would have accomplished what he did in 

 an experimental way under the difficulties which beset 

 him, and his work affords a good example of how a rela- 

 tively large amount can be accomplished by even a little 

 time given continuously. Entirely aside from any abso- 

 lute value which these books may have, they were an 

 important contribution at that stage in the development 

 of plant physiology, to the literature on the subjects on 

 which they touched. No man with a less well developed 

 faculty for detail and continued effort could have kept 

 the thread of the work so well, despite the many inter- 

 ruptions to which it was subjected. Their value, it may 

 be said, is more to botanical science than a merely senti- 

 mental one— it is rather in many respects one of real 



