i893. ON EPIPHYTES. 185 



unless indeed the tree have deciduous leaves (South Brazilian fig 

 trees), in which case numerous Epiphytes occur. 



The nature of the surface of a plant also determines the number and 

 sort of Epiphytes which lodge on it. Only a few forms can exist 

 on very smooth surfaces. These are chiefly Bromeliaceae, which may 

 be found on polished stems of palms, in glassy shoots of bamboos, 

 on leaves, and on smooth aerial roots. They are the pioneers 

 among Epiphytes, as they germinate on smooth spots unsuitable to 

 other forms. Among their roots these more exacting plants settle, 

 so that a colony of Epiphytes springs up round the originally solitary 

 bromeliad. 



On the other hand, there are forms which cannot live except on 

 very uneven surfaces, on rough or mossy bark, in the persistent leaf- 

 sheaths of palms (especially ferns). 



Most Epiphytes avoid trees with a peeling or scaling bark. 



In addition, the distribution of Epiphytes on plants depends on 

 causes not yet understood. For instance, an epiphytic orchid in 

 North Florida especially affects Magnolias. Crescentia ciijete is a 

 tropical American tree which is the greatest favourite with Epiphytes. 

 Schimper suggests that this is due to the facility with which root-hairs 

 penetrate its soft superficial cork. 



The Evolution of Epiphytes. 



We are now in a position to trace out the mode in which terres- 

 trial plants became Epiphytes in tropical America, and similarly in 

 other tropical regions. 



In the primaeval forests one sees terrestrial forms allied to the 

 epiphytic species growing at different heights up the trees. This is 

 not so in the open country, say in the savannahs, where the 

 Epiphytes are allied to those occurring in the tops of the trees in the 

 forests. This fact, and the general principle that moisture of the air 

 largely determines the presence, or absence, of Epiphytes, leads us 

 to the result that Epiphytes were evolved in the regions of moisture 

 — the forests. 



There are now species which grow in the forests as terrestrial 

 plants or as Epiphytes, but in the latter case they invariably grow in 

 moist gloomy spots on the lower part of trees; and, in general, 

 shade-loving forms occupying positions low down on the trees are the 

 simplest and least modified Epiphytes. They are the most recent 

 recruits in many cases. 



Thus to us comes the idea that when Epiphytes started their 

 aerial mode of existence, they commenced in these shady moist 

 positions not far above the ground. I may suggest that this view c f 

 Schimper's receives support when one particular group of Epiphytes 

 s considered — that is, the group in which some of the roots descend 

 to the ground, often having to be more than a hundred feet long to 

 attain this. The evolution of such roots is absolutely inconceivable. 



