PLANT SOCIETIES 
373 
upright leaves of the grass, which grows thickly crowded 
together, the broad leaves of the trees, and the leaves of 
the ivy, which grows on walls, arranged like a mosaic. 
Many divisions of the mesophytes might be made, for some 
prefer sunny locations, others shady places, and so on. 
Plants which live in the air make up another group, 
called epiphytes (ep'i-fites: Greek, epi, upon; phyton , a 
plant) because they usually attach themselves to the stem 
of a larger plant. Their modifications consist of one kind 
Figure 346. — Long-spurred Violet, a Mesophyte. 
of roots for fixing them to their support and another capable 
of absorbing and storing water. The latter organs are called 
velamens and are composed of spongy tissue. They are 
situated on the outside of the plant, their work being to soak 
up rain and dew and conduct it to an inner region where it is 
used as the plant needs it. Velamens can also absorb moisture 
from the air. The epiphytes are characteristic of the tropics, 
where the air is full of moisture and where rains fall frequently. 
In our own part of the world, lichens have somewhat the 
same habit, and orchids in greenhouses are another example. 
