n] 



WATER STORAGE 



43 



cases of this are seen in Polypodiiun sinuatiim and Lecanopteris carnosa, 

 which grow on exposed rocks and tree-trunks (Fig. 50). Their stocks are 

 distended while young by aqueous parenchyma. This dries up in the mature 

 state forming hollow galleries in which ants habitually live. These galleries 

 communicate with the outer air by passages excavated by the ants them- 

 selves at points corresponding to lateral buds, where the tis3,ues are soft. 

 The condition of these epiphytic Ferns is similar to that of Myrmecodia, 

 Hydnophytum, or Humboldtia. As in these Flowering Plants, the ants by 



Fig. 50. Lecanopteris cm-nosa, Bl. A = habit of the plant ; j9 = marginal flap, with sorus, enlarged ; 

 (7 = segment of a fertile leaf. {A, after Burck ; B, C, after Diels.) 



gnawing provide the entrance : they are the invaders, and there is no evidence 

 of the adaptation of the plant directly to the convenience of its visitors. 



The tubers of Nephrolepis have already been mentioned as containing a 

 carbohydrate store. They are also reservoirs for water, and it has been noted 

 that as they shrink under extreme drought the leaves wither, and the pinnae 

 are shed from the leaf-tops downwards, thus gradually reducing their exposed 

 surface. Still more remarkable provisions against drought are seen in Poly- 

 podium Brunei and bifrons, as described by Christ (Fig. 5 1 ). These epiphytic 

 Ferns produce pouch-like urns in form not unlike thoseof the Asclepiadaceous 

 plant Dischidia. Being hollow they naturally collect water when it is avail- 



