VARIETY AND TYPES IN NATURE. 
223 
perceptibly from those borne on the lower branches 
and those on the north side of the tree often differ 
from the ones on the south side. 
Professor K-, a Swiss naturalist, learned in 
college that there were at least fifteen species of oaks 
in the genus quercus. As most scholars did in the 
past, he studied from the specimens found in the 
herbarium. This is, of course, made up of only typi¬ 
cal leaves and flowers. When he went out into the 
forest to study the trees themselves, he soon found on 
one tree two leaf types, on another three, and so on, 
till finally he discovered the entire number on a sin¬ 
gle tree. His fifteen species naturally enough dwin¬ 
dled down to one. 
Equally great differences are quite as evident in 
flowers. The daisies, columbine, and honeysuckle 
seem to vie with each other in producing new shapes. 
Quite as puzzling are the asters. It is no easy matter 
to group them, and say this belongs to one species and 
that to another. 
When Prof. Asa Gray first described the asters of 
North America he classified them into about thirty 
species. In his late years he gave it as his opinion 
that there was only one species, and that all the 
others were probably only varieties of that one. 
The same thing has often been observed by other 
naturalists. There is everywhere a gradual shading 
of one variety into another, one species into another, 
and, to some extent, one genus into another. There 
are no distinct steps but a regular progression. 
The differences are often so minute that the expert 
