CLIMATIC DISTRIBUTION OF CERTAIN ANGIOSPERM LEAVES 
33 
Table IV — Continued. 
Rubiaceae .... 
Caprifoliaceae . 
Valerianaceae . 
Dipsacaceae . . . 
Cucurbitaceae . 
Goodeniaceae . 
Compositae . . . 
4 
39 
4 
H 
845 
1,261 
59 
15 
1,196 
70 
119 
253 
38 
3>i64 
610 
7 
26 
33 
33 
28 
1.471 
ledonous families, there is in almost all cases an obvious correlation 
between leaf form and environment. For example, such typical 
entire leaved woody groups as the Anonaceae, Lauraceae, Ebenaceae, 
Guttiferae, Rhizophoraceae, Myristicaceae, Sapotaceae, Apocynaceae, 
etc., are piactically absent from mesophytic cold-temperate regions, 
as are such characteristically non-entire families as the Betulaceae, 
Aceraceae, Platanaceae, etc., from lowland-tropical areas. Particu- 
larly significant, however, is the distribution of those families, Mal- 
vaceae, Rosaceae, Ulmaceae, Fagaceae, Tiliaceae, Leguminosae, etc., 
which possess both types of leaf-margins. The non-entire types 
usually reach their optimum development in mesophytic temperate, 
cool upland, or equable environments, the entire types in lowland- 
tropical or physiologically dry habitats, and the transitional forms in 
intermediate environments. To endeavor to explain all these correla- 
tions between leaf form and environment as mere coincidences would 
be very difficult. When it is taken into consideration, accordingly, 
that correlations between leaf form and environment occur in numer- 
ous famihes, genera, and even species, and in all paits of the tropical, 
temperate, and frigid zones, the effects of environment are clearly 
demonstrated. 
Although the form of the leaf-margin of Dicotyledons appears to 
be very strongly influenced by environment, historical factors and 
those influences of heredity which tend to maintain existing characters, 
are, of course, by no means inoperative. In any region, not all species 
will have been subject to the effects of prevailing climatic conditions 
for equal lengths of time or an equal number of generations; nor is it 
necessary to suppose that all species or groups of plants will respond 
with equal rapidity or in an exactly similar manner to influences of 
environment. Thus, the limited number of non-entire leaved types 
in lowland-tropical environments and the comparatively few entire- 
