THE NEW FIELD-BOTANY 357 



obtained in solution in the water. Hydrophytes have a 

 very considerable internal air space, thin cuticles through 

 which absorption is easy, and a greatly reduced vascular 

 system. 



Hygrophytes (Gr. hygros, moist) are land - plants 

 adapted to very moist conditions, such as obtain in 

 marshes, bogs, and the margins of ponds and lakes. 



Mesophytes (Grr. mesos, middle) occupy an inter- 

 mediate position between hygrophytes and xerophytes. 



Xerophytes (Gr. xeros, dry) are land-plants which are 

 able, by virtue of their structure, to endure periods of 

 drought and to flourish on dry soils. They have par- 

 ticular means of preventing loss of water by excessive 

 transpiration, which might be induced by heat, a dry 

 atmosphere, wind, and intense light. These means are 

 varied, including reduction of leaves to spines, as in the 

 Cacti and Gorse, or the development of fleshy stems and 

 leaves, as in the Stonecrops (Sedum). AU desert and 

 rock-plants are xerophytes. They are also adapted to 

 conditions calculated to reduce root-absorption, such as 

 the presence of salt and humic acid in the soil, or a cold 

 or dry soil. Many xerophytes occur in swamps and 

 aalt-marshes where water, of a sort, is plentiful, but it is 

 not of the quality required by hygrophytes; it may be 

 heavily charged with humic acid or with salt, and were 

 not absorption and transpiration severely checked, these 

 substances would enter the plants in disastrous quan- 

 tities. 



Most British plants are classed as Tropophytes (Gr. 

 tropos, change) ; they are so named because they manifest 

 different characters in summer and winter. Our decid- 

 uous trees are tropophytes. In summer they are vege- 



