286 PRACTICAL COURSE IN BOTANY 
that have adapted themselves to the presence in the soil 
or in the atmospheric vapor, of certain minerals, popularly 
known as salts, which cause them to take on many xero- 
phyte characteristics. The reason for this, as was shown in 
Exp. 39, is because the mixture of salt in the water of the 
soil increases its density so that it is difficult for the plant to 
absorb as much as it needs, and thus halophytes are living 
under “‘ physiologically ” xerophyte conditions. If you have 
ever spent any time at the seashore, you cannot fail to have 
observed the thick and fleshy habit exhibited by many of 
the plants growing there, such as the samphire, sea purslane 
(Sesuvium), and sea rocket (Cakile). A form of goldenrod 
found by the seashore has thick, fleshy leaves, and is as hard 
to dry as some of the fleshy xerophytes. 
Another characteristic of desert plants that is common 
also to seaside vegetation is the frequent occurrence of a 
thick, hard epidermis, as in the sea lavender and saw grass. 
The live oaks, trees that love the salt air and never flourish 
well beyond reach of the sea breezes, have small, thick, 
hard leaves, very like those of the stunted oaks that grow on 
the dry hills of California. The presence of spines and 
hairs, it will be observed, is also very common; e.g. the sal- 
sola, the sea oxeye, and the low primrose (Z’nothera humi- 
fusa). In other cases the leaf blades are so strongly involute 
or revolute (202) as to make them appear cylindrical. All 
these, it will be observed, are xerophyte adaptations, and the 
object in both cases is the same — the conservation of mois- 
ture. 
324. Mesophytes. — These embrace the great body of 
plants growing under the ordinary conditions of temperate 
regions, which may vary from the liberal water supply of 
low meadows and shady forests to the almost desert barren- 
ness of dusty lanes and gullied, treeless hillsides. The 
forms and conditions they present are so varied that it would 
be impracticable to consider them all in a work like this, but 
they may be summed up under the two general heads of 
