1gto] WIEGAND—TRANSPIRATION 431 
of such coverings is considered. In the absence of such evidence 
the following questions have frequently occurred to the writer: 
1. Do such coverings actually retard the loss of water sufficiently 
to justify their maintenance on this basis through natural selection ? 
2. Is it not highly improbable that coverings so thin as are “‘strigose”’ 
coverings should affect the loss of water in any way, and does not 
this count as an objection to the water-retarding theory? 3. If 
the function of hairs is to retard the loss of water, why should some 
plants employ thick cutin and others a resinous coating instead of 
plant hairs to attain the same end? 4. Has the relation to light or 
the relation to loss of water been the principal factor in the evolution 
of hairy coverings? Since the answering of these questions has 
seemed to be of rather fundamental importance in the teaching 
of ecology, an attempt has been made to obtain evidence, either 
circumstantial or direct, and the results obtained form the basis of 
this paper. 
The few actual experiments with hairy coverings, so far as I 
have been able to find, may be summarized as follows. KERNER? 
bound two raspberry leaves around two thermometer bulbs in such 
a way that in one case the green upper leaf surface and in the other 
case the white tomentose under surface was outermost. When 
placed in the sun, the mercury in the green bulb rose to a point 2-5° 
above that in the white bulb.’ Two more raspberry leaves were 
entirely removed from the plant and laid side by side in the sun. 
The one with the green surface uppermost dried and shriveled much 
Sooner than the one with the white surface uppermost. GOEBELER* 
investigated the effect of trichome structures on the stems of ferns. 
He found by weighing that the living trichomes markedly increased 
the transpiration. Vesque* found by means of cultural -experi- 
ments with certain plants that when the dryness increased, the hairy 
covering increased in density also. BRENNER‘ found that the hairy 
? KERNER, A., AND OLIVER, F. W., The natural history of plants 1:314. 
3 eS E., Die Schutzvorrichtungen am Stammscheitel der Farne. Flora 
69:487. 1 
*. 4 VEsQuE, M. J., ET Viet, M. C., De linfluence du milieu sur la structure ana- 
tomique pe vittiiscs Ann. Sci. Nat. Bot. VI. 12:176. 1881. 
5 BRENNER, M., see BURGERSTEIN, Die Transpiration der Pflanzen 210. 1904. 
