i8 9 3- ON EPIPHYTES. 175 



its periphery swollen. In this manner a species of adhesive disk is 

 formed and applied closely to the uneven surface of the host. The 

 attachment is rendered all the firmer by the formation of numerous 

 root-hairs radiating from the peripheral swelling. 



Thus the whole root-system of an Epiphyte — except at a very 

 early stage of germination — is adventitious. The same is the case 

 with shrubs growing in our own climate on rocks or walls. In both 

 cases this is obviously the direct effect of the mode of life. 



The flowers of Epiphytes display no adaptive characters. 



Concerning the modes of reproduction, vegetative multiplication 

 is frequent. The case of Tillandsia usnevides is interesting. Its pendent 

 shoots are either whisked away by the wind or carried away by birds 

 for the purpose of constructing nests. The transferred fragments 

 send out new shoots, which twine round the branches of the new host. 

 This Tillandsia only rarely produces flowers. 



It is in the structural characters of the vegetative organs that 

 Epiphytes display the greatest amount of adaptation. 



Epiphytes grow in situations where the supply of nutritive 

 solutions is meagre and fluctuating, and where, usually, only diffused 

 light reaches them. Moreover, they live in positions in which firm 

 support is essential. For fixation and the absorption of nutritive 

 solutions, a strong development of surface of the root-system is 

 indispensable. Owing to the poverty of their water-supply, measures 

 must be taken to avoid excessive transpiration. A desert plant 

 accomplishes this by diminishing its transpiring surface; but an Epiphyte 

 cannot afford to act similarly, because it requires a large assimilatory 

 surface in order to make up for the weakness of its illumination. The 

 Cactaceae illustrate this point. The desert forms often have swollen, 

 rounded shoots which are sparsely branched ; but the epiphytic 

 forms possess fiat, leaf-like shoots (Phy Hoc actus, Epiphyllum), or have 

 numerous thin branches (Rhipsalis, Cassytha). It only remains, then, 

 for the Epiphytes to have leaves constructed so as to retain their 

 supply of water. Hence the leaves are often leathery or fleshy, and 

 frequently have a strong development of cuticle. 



The mode in which Epiphytes absorb nutritive solutions serves 

 as a basis for their classification. Appended is a brief table to show 

 the grouping: — 



Class I. — Epiphytes which absorb the nutritive solutions by means of their 



wots. 



Group (i.) Those which content themselves with utilising the 

 water and humus occurring on the surface of the host-plant. 



Group (ii.) Those which have attaching roots and also absorp- 

 tive roots which descend to the ground. 



Group (iii.) Those which have arrangements for collecting water 

 and humus. 



