202 
THE PLANT WORLD. 
Torrey along systematic lines, but his extensive knowledge of 
plants led to special studies of the problems of distribution and 
adaptation. Early in his career Gray won the friendship and con¬ 
fidence of Darwin and later became one of the chief exponents 
of the theory of natural selection in America. 
Gray’s memoir, published in 1859, on the botany of Japan in 
its relations to that of North America fixed the attention of the 
world on him as a philosophical naturalist. It showed that he 
could make excursions into the realm of ideas as well as that of 
plants. 
Among other essays which deal with ecological subjects were 
the following: Do Varieties Wear Out or Tend to Wear Out?; 
Forest Geography and Archaeology; The Pertinacity and Pre¬ 
dominance of Weeds; The Characteristics of the North Ameri¬ 
can Flora. I11 addition to the well-known Manual, Dr. Gray 
planned and started the Synoptical Flora of North America which 
has since been carried on by Watson and Robinson. 
The importance of the work which Torrey, Gray, Watson, and 
Coulter did for ecology was in describing and systematizing the 
plants of this country. Upon this foundation all subsequent work 
in plant distribution and physiographic ecology rests. 
We are indebted to Engelmann not only for a classification of 
several difficult groups, e. g., the conifers and oaks, but also for 
a knowledge of the habits of some of our western plants. As 
examples of the latter, we may mention his monograph of the 
yuccas published in 1873 describing the symbiotic relations of the 
plants with the insects which pollinate their flowers. Engelmann 
was a physician of large practice in the city of St. Eouis who 
spent much of his time in the pursuit of botany. It is related 
that he even busied himself drawing cacti while diagnosing the 
cases of his patients. 
American botany has produced several important monographs 
on the flora of particular regions. 
Chapman’s Flora of the Southern United States was one of the 
first of this class, both in point of importance and of time. The 
first edition appeared in i860, and a second revised edition in 
1897, j us t two years before his death. It will always remain a 
