1900]. Leavitt, — Relation of plants to atmospheric moisture 29 
II. DEWBERRY. Stems trailing, but in the first three species occasionally 
erect, recurving to the ground if elongate. 
A. Leaflets oval or ovate, acute or pointed, dull, usually somewhat 
pubescent beneath; pedicels long and ascending; prickles stiff. 
I. Branches few- to several-flowered. 
a. Leaflets large, thin, coarsely and simply toothed, terminal one 
usually rounded at the base; flowers and fruit large; stems 
stout with tall branches. R. invisus. 
A Leaflets firm, sharply and somewhat doubly toothed; plant 
every way smaller. R. villosus. 
2. Branches 1-flowered (sometimes 2-flowered); leaflets thin; stems 
slender, with few minute prickles. R. Enslenii. 
B. Leaflets obovate, blunt, glabrous, shining; pedicels in flower short, 
divergent; flowers and fruit small; stems slender, with small, 
weak bristles. R. hispidus. 
(Trailing forms of 2. setosus may be looked for here and may be separated by 
the acute, dull leaves and larger flowers.) 
THE RELATION OF CERTAIN PLANTS TO ATMOSPHERIC 
MOISTURE. 
ROBERT G. LEAVITT. 
Oncuips. In making some tests of absorption by orchids, in the 
interests of the scientific side of practical gardening, I was surprised to 
find little or none of the power of condensing water-vapor which is 
popularly ascribed to the aérial roots of epiphytes. Not the public 
alone, but gardeners universally, and botanists pretty generally, regard 
air-plants as capable of * feeding upon the air." The highest author- 
ity, too, may be cited in support of such an opinion. Thus Sachs‘ 
says, “ The walls [of the velamen] are capable of imbibing, and are 
able to absorb, not only rain and dew but even the vapor of the at- 
. mosphere.” Kerner, the popularity of whose Natural History of 
Plants gives his opinions wide vogue, is explicit in the assertion that 
*the power of condensing aqueous vapor, and other gases as well, is 
. of the greatest importance to these plants." He repeats and amplifies 
this at considerable length. 
The doctrine of vapor-absorption goes back to the experimental 
work of Unger? (1854) and Leitgeb* (1864). The contrary view 
was expressed, after experimentation, by Duchartre5 (1856). He 
says that “the leaves do not breathe in the vapor of water diffused in 
1 Phys. of Plants, Eng. Tr., 1887, p. 25. 2 Natural History of Plants, Vol. I., p. 222. 
3 Physiologie der Gewiichse, 1855, p. 307. 4 Denkschr. d. Wiener Akad., 1864, p. 215. 
5 Quoted, Bull. de la Soc. Bot. de Fr., 1895, s. 3, t. II, p. 99. 
