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 (CEnothera humi- 

 fusa). In other cases the leaf blades are so strongly involute 

 or re volute (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 



