THE RELATION OF HAIRY AND CUTINIZED 
COVERINGS TO TRANSPIRATION 
KARL M. WIEGAND 
(WITH ONE FIGURE) 
Numerous experiments have shown that cutin is a very efficient 
means of retarding the loss of water from plant tissue. We may cite 
only such cases as the paring of the apple and its consequent much 
increased loss of water as shown by weighing, and of various other 
plant tissues similarly treated. In regard to the function of hairy 
coverings, however, the lack of experimentation has left us very much 
in doubt. We find two theories advanced: one holding that such 
coverings are to retard transpiration, the other that they are to pro- 
tect the tissue from too intense light. Some have held also that they 
may, and probably do, serve both purposes, either at the same time 
or in different cases. 
It has long been recognized that hairy coverings must be divided 
into two classes when function is considered, namely the living and 
the non-living.!. The cells of the former contain protoplasm, and 
therefore are themselves in danger of drying out. Such hairs natu 
rally cannot be used by the plant for restricting loss of water. The 
non-living hairs, however, are soon free of protoplasmic contents 
and are filled with air. In such a form, spread out over the plant 
surface, they may well be conceived of as constituting a restricting 
screen to the passage of water vapor. By the refraction of light 
from the contained air this type of hair may also act as a light screen. 
We shall have to do, therefore, only with this latter group in the fol- 
lowing pages. : 
Experimental evidence for or against either of these theorles 
of the function of air-containing plant hairs is very meager, however 
and this is the more remarkable when the very common occurrence 
« FLEISCHER, E., Die Schutzeinrichtungen der Pflanzenblatter gegen Vertrock: 
nung. 16, Bericht. iiber das K. Realgymnas. zu Débeln. 188s. 
VoLkens, G., Die Flora der agyptisch-arabischen Wiste auf Grundlage 
anatomisch-physiologischer Forschungen. Berlin. 1887. 
Botanical Gazette, vol. 49] [43° 
