TRICHOME-HYDATHODES 



491 



subterminal cell ; as a matter of fact, this wall is provided with numerous 

 slit-like pits. The final exudation of the water must take place by 

 filtration through the lateral walls of the dead terminal cell. 



The leaves of Phascolus midtiflorns bear, especially on their lower 

 side, curved clavate hairs, which act as hydathodes (Fig. 195 b). Each 

 hair consists of a large, usually somewhat distended basal cell, super- 

 imposed upon which are several (most often four) layers of smaller 

 cells forming the club-shaped " body." As a rule the cells of the 



Trickome-hydathodes. 



Fig. 195. 



A. Machaerium oblongifoliv.m. B. Phaseolus multifiorus. 

 C. Piper nigrum. 



uppermost tier are divided in two by median walls. All the cells have 

 thin lateral walls and abundant protoplasmic contents. Neither the 

 cavities nor the membranes show any trace of oily, resinous or gummy 

 secretion. In many Piperaceae (Fig. 195 c), Bignoniaceae and 

 Convolvulaceae, in species of Artocarpus, etc., the hydathodes take the 

 shape of shortly stalked capitate or scutate hairs. While varying 

 greatly in detail, hydathodes of this type always consist of three 

 portions, namely, a head or scale, a stalk and a base or foot. The uni- 

 or multicellular head is responsible for the actual secretion of the 

 water. Here the external cell-walls are unthickened and covered by 

 a very thin and pervious cuticle, which sometimes becomes distended 

 and finally ruptured owing to the formation of a mucilaginous substance 

 within the wall. In certain Convolvulaceae (Stictocardia tiliacfolia, 

 Opercidina Twpethum), according to Svedelius, the cuticle is perforated 

 by minute pores. The stalk-cell may be regarded as the mechanical 



