i893. ON EPIPHYTES. 179 



retention of decaying humus-giving bodies, and the roots frequently 

 branch copiously in the air, some of them deserting the surface of 

 the host. 



In many epiphytic orchids there are attaching roots which are 

 negatively heliotropic, and in addition clusters of erect negatively 

 geotropic roots which are wholly absorptive in function. In orchid 

 houses, potted specimens of these orchids frequently possess roots 

 growing vertically upwards out of the soil (species of Cymbidium, 

 Eulophia) ; but there is no reason to believe that these roots act 

 thus in order to supply the subterranean parts with oxygen. They 

 simply point upwards because, when the plants are growing in their 

 natural position (as Epiphytes), the nutritive materials come from 

 above, and are absorbed by these peculiar roots. 



An aroid, Anthuvium Hiigelii, is a good type of an Epiphyte 

 belonging to this group. Although a large plant, it is often to be 

 found fastened to the smooth aerial roots of Clusia, or to the band-like 

 stems of Bauhinia. It is fixed to its support by means of very long 

 roots, which stretch along the surface of the host and give off root- 

 hairs only on the side towards the latter. An extensive rounded 

 complex of roots surrounds and overtops the dwarfed stem, and gives 

 off numerous lateralroots among the sub-sessile leaves. The last-named 

 form a large rosette enclosing a mass of vegetable fragments, which 

 decompose into humus. The complex is composed mainly of much 

 branched and hairy nutritive roots which are closely interlaced at 

 their bases, but which possess apices freely protruding into the air or 

 dipping into the humus. 



In this plant, as in the rest of this group of Epiphytes, the 

 structural differences between the attaching and nutritive roots are 

 not so wide as in the second group. This is due to the fact that the 

 attaching roots absorb water to a certain extent, and that the nutritive 

 roots do not conduct the absorbed substances over long distances. 

 Still, the nutritive roots of Anthurium Hiigelii possess larger and more 

 numerous vessels and fewer sclerenchyma-fibres than do the 

 attaching-roots. 



Some ferns have precisely similar arrangements, e.g., Polypodium 

 phy llitidis. 



In other ferns the humus is collected by single leaves which 

 form pockets against the surface of the host's stem, or against their 

 own stems. In Polypodium quercifolium (3) the differentiation has gone 

 so far that there are two sorts of leaves : in the first place, ordinary 

 stalked pinnate leaves ; secondly, sessile negatively geotropic leaves, 

 which form pockets against the opposed surface. The latter assimilate 

 only for a brief period, but persist as large, dead, yellow oak-like 

 leaves. Thus when dead they do not drop off (as do the normal 

 foliage leaves), but, being strongly ribbed, persist as receptacles for 

 humus. 



Another heterophyllous Epiphyte is the curious twining, pitchered 



N 2 



