DARWIN MEMORIAL CELEBRATION 
33 
of pangenesis, an ingenious supposition, applying to living matter the general 
features of the atomic theory, with an additional inherent power of repro¬ 
duction of the atoms or “gemmules” as he termed the hypothetical ultimate 
particles. 
The movements of plants and of their various organs were also studied 
by Darwin for many years. His first essay on this topic appeared in 1865 
and ten years later he revised and enlarged it 'as a book under the title 
“The Movements and Habits of Climbing Plants,” using, as always, not 
only his own detailed and extensive observations, but also the published 
writings of other botanists, among them the paper on tendrils by Hugo 
de Vries, who was destined subsequently to throw such a flood of light on 
the phenomena of variation. Darwin grouped climbing plants into twiners, 
leaf-climbers, tendril-bearers, hook-climbers and root-climbers. He main¬ 
tained that the climbing habit has been developed to enable vines to reach 
the light and free air; tropical forests show conclusively that this is the case. 
He showed that circumnutation, the bending of growing tips successively 
to ail points of the compass, is a general phenomenon among flowering 
plants, and he thought it of high importance to them. The sensitiveness 
of tendrils to external influences interested him deeply, and he made many 
original experiments upon them. Following the subject much further he 
published in 1880 the work entitled “The Power of Movement in Plants,” 
a treatise abounding in records of original observations on seedlings and 
parts of mature plants, including further studies of circumnutation, of the 
sensitiveness of plants to light and to other forces and of the phenomena of 
geotropism and apogeotropism, which he regarded as modified phenomena 
of circumnutation. 
The value of the impulse given by Darwin to botanical investigation 
in all its branches is beyond estimation; his power of exact observation 
and record has seldom been equaled and certainly never excelled; his 
deductions were highly philosophical, and most of them have stood the 
test of thirty years’ inquiry and criticism; he was searching for truth and 
his absolute honesty in research is plainly evidenced by his repeated criticism 
of his own conclusions. 
The immense number of plant species which had been described and 
named, and the lack of any complete index to them led Darwin to provide 
in his will for complete enumeration of the names of published species of 
flowering plants. This great work was prepared at the library of the Royal 
Gardens, Kew, England, and published in 1895 in four large quarto volumes, 
to which several supplements have since been added. This “Index 
Kewensis” is a great boon to all investigators, and is quite indispensable 
to those who have to take plant names into consideration. 
