EPIPHYTES OR AIR PLANTS. 131 
stem or branches descend to the ground, and fixing themselves 
there, not only act as mechanical supports, but also assist the 
true root in obtaining food. Such roots are well seen in the 
Screw-pine (fig. 199, 2), in the Banyan or Indian Fig-tree 
(fig. 254), and in the Man- 
grove-tree (fig. 255). In the 
latter tree these aerial roots 
frequently form the entire 
support of the stem, both me- 
chanically and otherwise, in 
consequence of this decaying 
at its lower part. 
Epiphytes or Air-plants.— 
In these plants none but aerial 
roots are produced (fig. 256, 
a, a), and as these never reach 
the soil they cannot obtain any 
food from it, but must draw 
their food entirely from the air 
in which they are developed ; 
hence the name of air-plants 
which is applied tothem. They 
are also called epiphytes, be- 
cause they commonly erow Fig. 255, The Mangrove-trce (Ithizophora 
upon other plants. Most Or- a ea 
chids (fig. 256) and Tillandsias afford us illustrations of epiphy- 
tical plants. The roots of such plants are commonly green, and 
possess a true epidermis and stomata ; in which particulars, there- 
Fie. 255. 
Fie. 256. £ 
if i" | 
iy ZL 
Fig, 256. Orchidaceous plants, to show their mode of growth. a, a. Aerial 
roots. 0, 6. Pseudobulbs. 
fore, these aerial roots present exceptions, as already noticed, to 
what is commonly observed in other roots. The aerial roots of 
Orchids have also a layer of usually very delicate fibrous cells 
K 2 
