1910] WIEGAND—TRANSPIRATION 437 
also greater than that of cutin in this respect. Their relative effi- 
ciency in wind is not markedly different, whether the sun shines or 
not (series II and IIA, column 6), being somewhat less perhaps in 
the former case. Their actual protection, of course, is greater the 
larger the quantity of water lost, i.e., in wind and in sunlight. 
Some experiments were conducted with shellac in the place of 
the waxy coating on the blotter. The shellac was considered to 
represent more nearly the resinous coatings so frequently spread 
over leaves and twigs in dry regions. The readings showed the 
behavior of waxy and resinous coatings to. be very similar. 
* a 
CSF pte ce ee oe ere ves ANS 
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MAM NGWH 
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G. 1.—Diagrams illustrating the relation of evaporation from oer and hair- 
covered surfaces i in wind and in still air: gq, hair-covered in still air; 6, naked in still 
air; c, hair-covered in wind; d, naked in win 
Many readings were taken with actual leaves substituted for the 
blotters, but in the main they were very erratic. It was found, 
however, that leaves of Hydrangea and of Nicotiana especially, 
when covered with layers of cloth and cotton, behaved essentially 
the same as did the blotting papers. Probably all would have done 
so if the other factors could have been eliminated. 
The reason for the slight efficiency of hairy coverings in still air 
and their greatly increased efficiency in wind is not at first apparent. 
The following is the only plausible theory occurring to me. As 
indicated in the accompanying diagrammatic drawings, in still air a 
layer of nearly saturated air is soon formed and maintained above 
the naked as well as above the hair-covered blotter (jig. 7, a and 6). 
[f the hair is thin, it is imbedded in this layer, and the latter is modified 
little if at all by the hair. Evaporation, therefore, with or without 
the hair, is into an atmosphere of about equal saturation, and there- 
fore should be about the same. If the hair is very thick, then the 
