154 SOUTH AFRICAN BOTANY 
all the ground just around the-plant and causes the 
extinction of any other seedlings; others having quick- 
growing underground stems. Most of them have self- 
pollinated flowers, so that they are certain to set seed, 
and most have excellent methods of seed-dispersal either 
by wind or by animals, 
In the same way, if the plants of any particular 
district be examined, they will probably show certain 
characteristics which specially fit them to live in those 
particular surroundings. From this point of view we 
may group plants into :— 
1. Xerophytes, which are adapted for life in very dry 
places. 
2. Hydrophytes, which live in water or marshes. 
3. Mesophytes, which are the ordinary land plants, 
and 
4. Epiphytes, which live on other plants, but do not 
take any nourishment from them. 
188. Xerophytes.—These are plants which can live 
with a very small supply of water, and therefore they 
are found in places where there is a long dry season, or 
where the soil ig very sandy, so that the water all runs 
through it. They are also found on rocky ground, 
where there is again a scanty supply of water; on the 
sea shore, where the presence of an excess of salt in the 
soil hinders absorption by the roots; and on high 
mountains, where the plants are exposed to drying 
winds. In all these places the plants have to check 
transpiration without preventing assimilation ; a difficult 
problem, since the same conditions are favourable to 
both functions. We find that different plants have 
