86 
THE AMERICAN BOTANIST 
normally terrestrial are often found in such situations. It has 
been well said that Nature has very few unoccupied places, and 
these plants have established themselves there because the condi- 
tions are favorable. 
The plants which we are particularly speaking of are largely 
tropical and sub-tropical. In cold regions the plants that grow in 
the mould of the bark are for the most part mosses, liverworts 
and lichens, but in the tropics such situations form the rallying 
ground for a host of ferns and flowering plants. Small ferns are 
so numerous as to wreath the trunks, and with these are found 
Aroidese, Orchids, Bromeliads, etc. It has been remarked that 
the Bromeliads chiefly ornament the forks of the trunks, while 
Orchids, Dorsteniese and the various species of RJiipsalis grow on 
the upper surfaces of branches that ramify horizontally, while 
Aroidae and begonias take root for the most part on the surfaces 
of high erect trunks. 
The bark itself, that is the cortical layer, dead, but not yet 
crumbled and mouldered into dust, forms a nutriment substratum 
for a series of plants of various aflinity — lichens, fungi, mosses, 
and higher plants. Even in the case of tropical orchids growing 
on a substratum of bark, if the roots are forcibly detached, little 
fragments of the bark will be found torn off with the rhizoids at 
the places where they issue from the stems. The majority no 
doubt nestle in the mould-filled crevices in the bark, and nourish 
themselves, besides, by means of special aerial roots which hang 
d»o(\vn in white ropes and threads, like a mane, from the places 
where the plants are situated. Some of these roots are flattened, 
and adhere firmly to the bark with their flat surface, like the roots 
of Phal^nopsis Schillcriana, and on the under surface, behind the 
growing point, is a whitish fur, consisting of short, thickly 
packed, absorptive cells, and these adhere so tightly that it is often 
easier to detach small pieces of the bark than the root itself. Sim- 
ilar conditions have been observed in the roots of many other 
epiphytes. A curious fact has been obser^xd in conection with 
these plants, namely, that when transferred to loose earth, devoid 
