250 BOTANICAL GAZETTE [OCTOBER 
The plants of warmer temperate climate (austro-riparian 
species) require a greater number of heat units than those plants 
just described, and their distribution at present depends largely 
upon temperature and soil conditions. In the case of the austro- 
riparian species found in the southern Appalachian mountains, 
two factors are probably most effective in permitting these 
species to maintain themselves in what would seem to be an 
unfriendly environment, viz., amount of insolation and the nature 
of the soil.?? 
A favorite situation in the mountains for colonies of lower 
austral species is on the southern exposure of hills, where 
the angle of inclination and the position with reference to the 
sun insure the greatest possible amount of insolation. The soil 
preferred by the great majority of these species is light, sandy, 
and poor in organic material; it is consequently readily perme- 
able to water and becomes quickly and strongly heated, being 
thus similar to the soils which cover a great part of the coastal 
plain. 
Unfortunately no phenologic data are at hand with reference 
to the plants of warmer temperate character. In lieu of exact 
data, a reference to Chapman’s Flora ® may assist in determining 
the position of these plants with reference to the period of 
flowering. Those plants not of neotropic origin, which are 
probably the more or less modified descendants of that char- 
acteristic flora which existed in Eocene and Miocene times, and 
species of genera that appear to be on the wane, blossom in gen- 
eral, according to Chapman, from May to July, and are not 
looked upon as spring plants, which blossom from March until 
May. The neotropic element in the flora of the eastern United 
States is represented by plants that bloom in general from June 
until October," and are therefore summer and autumn species. 
This result of a phenologic tabulation of the austro-riparian 
plants might have been expected, when the origin and physio- 
7? KEARNEY, (oc. cit. 841. 
*3 CHAPMAN, Flora of the southern United States. 3d ed. 
4 Another group of plants, derived like the Cactaceae and Compositae from the 
southwest, bloom at about the same period as the plants of neotropic origin. See my 
paper in Science, Joc. cit, 
