EPIPHYTES 
I 75 
been evolved from plants which originally climbed with 
clasping roots. 
In the third place, epiphytes are placed in conditions 
w r here the water-supply is small and precarious and easily 
runs away. No plants then can be regular epiphytes unless 
they possess well-marked xerophytic characters, including 
as a rule the capacity for water-storage. The Orchidaceae 
collect water by their aerial roots and store it in tubers or 
fleshy leaves ; Bromeliaceae have fleshy leaves and water- 
collecting pitchers ; ferns have fleshy stems and also gather 
much humus which retains water well ; ‘ aqueous tissue 7 in 
which water is stored occurs in the leaves of Aeschynanthus, 
Peperomia, &c. ; other arrangements occur in other species. 
Peculiar semi-epiphytism occurs in many Araceae ( q.v .) 
which have long nutritive roots descending to the soil, and 
in species of Clusia and Ficus. 
Most epiphytes obtain the mineral substances required for 
nutrition from decaying organic matter ( humus ), and many 
have interesting arrangements for its collection. In most 
forms a certain amount of dead leaves and other debris 
collect at the base of the plant ; in many ferns the leaves 
make niches against the support, e.g. in Polypodium sp. and 
Platy cerium, or form nests, as in Aspleninm nidus ; in Dis- 
chidia the pitchers collect humus, and also in Bromeliaceae. 
See Part II. 
Moisture seems everywhere an important factor in regu- 
lating the distribution of epiphytes. In deep ravines in 
Europe the trees may be seen loaded with epiphytic ferns, 
&c. Plants living on the soil in a tropical forest may 
similarly become epiphytic to this extent if they possess the 
necessary methods for seed-dispersal and anchorage of the 
seedlings. They may then gradually work higher up the 
trees, and thus get nearer to the light as they develope xero- 
phytic characters to enable them to stand the increased 
transpiration, and so on. In actual fact we find epiphytes 
with very pronounced xerophily on the very tops of trees, 
others with less marked characters lower down. On the 
savannahs of America, where the climate is drier, the 
species from the tops of the forest trees occur as epiphytes, 
but no others. These well-marked epiphytic species also 
occur as alpine forms in neighbouring mountains, but not 
