x OBITUARY 299 
carried home some plants, and on giving them 
some insects saw the movements of the tentacles, 
‘and this made me think it possible that the insects 
‘were caught for some special purpose. Fortu- 
nately, a crucial test occurred to me, that of placing 
a large number of leaves in various nitrogenous 
and non-nitrogenous fluids of equal density; and 
as soon as I found that the former alone excited 
energetic movements, it was obvious that here was 
‘a fine new field for investigation.” (I, p. 95.) 
The researches thus initiated led to the proof 
that plants are capable of secreting a digestive 
fluid like that of animals, and of profiting by the 
result of digestion ; whereby the peculiar appara- 
tuses of the insectivorous plants were brought 
‘within the scope of natural selection. Moreover, 
these inquiries widely enlarged our knowledge of 
the manner in which stimuli are transmitted in 
plants, and opened up a prospect of drawing closer 
the analogies between the motor processes of plants 
‘and those of animals. 
~ $o with respect to the books on “Climbing 
Plants” (1875), and on the “ Power of Movement 
im Plants” (1880), Darwin says ;— 
“T was led to take up this subject by reading a 
short paper by Asa Gray, published in 1858. He 
sent me some seeds, and on raising some plants I 
‘was so much fascinated and perplexed by the 
revolving movements of the tendrils and stems, 
which movements are really very simple, though 
