Polygonum Amphibium. 47 



hairs, about 0"7 mm. in length, make their appear- 

 ance on the epidermis of the leaves and stem. These 

 are set as closely together as possible, especially on 

 that part of the stem which bears the inflorescence, 

 and their globular terminal cells secrete a viscid 

 substance which causes the axis of the inflorescence 

 to be quite sticky to the touch. Such small wingless 

 creeping insects as might steal the nectar without 

 bringing the advantage of a cross to the flowers, cannot 

 get over this sticky axis. If they attempt to do so, 

 they are held fast as on bird-lime. Entrance to the 

 flower is therefore in these cases made impossible by 

 the secretion of a viscid' substance on the path which 

 leads to it. These sticky trichomes, as before remarked, 

 are absent when the plant is growing completely in 

 the water. If the ground on which a Polygonum has 

 grown for years in dryness, so as to have become 

 covered with these trichomes, again be flooded, and 

 the stems and peduncles again therefore be encircled 

 with water, the trichomes with their viscidity 

 disappear, and the epidermis again becomes smooth 

 and even. The water which surrounds the inflor- 

 escence is now a suflBcient protection, and the viscous 

 matter is therefore superfluous. 



I need hardly demonstrate in detail that it is 



from the epidermal cells, whatever their form or function ; root- 

 hairs, -woolly hairs, glandular hairs, prickles, paleas and sporangia 

 of ferns, etc., etc., are all included. — Editor.] 



