

Comparative Anatomy 



of the 



Filz-lite Hair-covering of Leaf-organs, 



This question was suggested to me by Prof. Schwen- 

 dener, who had observed that the under cells of the hairs 

 on certain leaves were thin-walled, also the epidermal 

 cells, while the wall of the upper hair cell or cells was 

 thickened, often to such an extent as nearly to fill the 

 lumen. Together with this peculiarity was noticed a 

 certain form of stoma which hitherto had been observed 

 only on leaves growing in a very moist atmosphere but 

 destitute of any hair covering. These two facts sug- 

 gested the probability of a connection between the hair- 

 covering and the ability of the leaf to take up moisture 

 in a liquid form from the atmosphere. 



Authorities agree in ascribing to this coating the 

 office of protection. This may be against too rapid trans- 

 piration in case the plant is exposed to sun and wind 

 and destined to endure a long dry season. The fact that 

 this coating is often on the under side of the leaf only, 

 where the greater number of stomata usually occur, sup- 

 ports this view of the function of the hair in these cases. 

 Protection may thus be given against injury to the chloro- 

 phyll through insolation ; this can apply only to a small 

 number of plants, namely, those whose leaves are coated 

 on both sides, or on the physiological upper side, or 



