446. ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
ideas, usually connected directly or indirectly with the theory of 
evolution, and sometimes extending and corroborating it more fully. 
I must at least give a few indications as to the nature of these dif- 
ferent books. 
In 1862 Darwin published his book, “The Various Contrivances 
by which Orchids are Fertilized by Insects.” Orchids often exhibit 
the most special and diverse adaptations to the visits of insects, and 
they help to make clear to us how flowers may have been developed 
in all their manifoldness in relation to the needs of their insect 
visitors. 
In the same year and those following there appeared several 
treatises on “ Dimorphism in the Flowers of Primula.” Darwin had 
discovered minute differences in the length of the stamens in the 
same species, and he demonstrated that these differences are not 
mere chance variations, but are adaptations which secure the crossing 
of individuals and prevent self-fertilization. He obtained the proof 
-of this through many careful experiments. 
This was followed, in 1864, by a treatise on “ The Movements and 
Habits of Climbing Plants,” showing the different ways in which 
they climb—another study in plant adaptations. In 1868 appeared 
the great work begun in 1860, “ The Variation of Plants and Animals 
under Domestication,” and this book greatly extended and strength- 
ened the basis of his theory of selection. The phenomena and laws 
of variation and heredity are discussed and illustrated by a wealth 
of examples, and the work concludes with a theory of heredity which 
he called “ Pangenesis.” 
“The Descent of Man” appeared in 1870. Up till that time 
Darwin had made no definite pronouncement upon this subject, 
though of course he must from the very first have deduced from 
the variability of species that man also was a product of evolution. 
He now discussed this view in detail in a two-volumed work, which 
also contained a fuller treatment of an aspect of the theory of 
selection only briefly sketched in “The Origin of Species.” Here 
the phenomena of “sexual selection” are traced throughout all the 
animal groups in which preferential mating plays a part. The 
principle is illustrated by a positively overwhelming mass of detailed 
facts, and is shown to have been a factor even in the differentiation 
of the sexes in the human race. 
Closely associated with this work is the one which followed it in 
1872 on “ The Expression of the Emotions in Man and in Animals.” 
The birth of Darwin’s first child in 1839 had induced him to record 
in a special notebook all his observations on the gradual awakening 
of the sensations, and their expression on the features of the child, 
for he was convinced that even the most complex and delicate 
emotional expressions of man had their natural roots in animals, 
