PLANT PHYSIOLOGY 157 
do flower, the flowers are formed above water as in the 
Water Lily. 
140. Hygrophytes. — Hygrophytes (moisture-loving) 
plants grow in marshes, or at the sides of rivers and 
streams, and they show characteristics intermediate 
between the truly aquatic plants and those which live 
on land. 
141. Epiphytes cling to other plants for support, 
but are not parasitic upon them. They abound in the 
tropics where the dense forests shut out the light from 
the ground beneath, so that small herbaceous plants 
must either become epiphytes or climbers. The epi- 
phytes, by their position, get plenty of light and air, 
but it is difficult for them to obtain the necessary water 
and salts. 
They all possess certain characteristics in common. 
Firstly, they must all have excellent methods of seed 
dispersal by either wind orbirds. Secondly, the seedling 
must be able to fasten itself to its support as soon as it 
germinates, and so we find epiphytes have clasping 
roots which are usually adventitious. Thirdly, these 
plants have but a small and precarious water supply, 
hence they show all kinds of xerophytic characters, 
especially the capacity for water-storage. 
Most epiphytes obtain the mineral subtances required 
for nutrition from decaying organic matter. 
142. Elongation of Root and Stem.—It will have been 
noticed when the germination of seeds was being ob- 
served, that the radicle and plumule both elongate 
rapidly after they emerge from the seed. ‘To find 
out in which part of the root and stem this elongation 
