Chap. I] 



WATER 



17 



regions with wet winters and dry summers, like that 

 of the Mediterranean. Finally, according to certain 

 authors, the dense cushion-like growth of certain plants 

 (Figs. 19, 20), which has not yet been mentioned, may 

 also be included among the protective measures against 

 drought ; amongst phanerogams this is confined to 

 plants of regions that are cold, or at any rate cool 

 and periodically cloudy, and is chiefly prevalent in 

 those of high mountains. A hard substratum appears 

 to favour it, but is not essential, for cushion-like vege- 

 tation is also found on meadows and moorlands. 



Such differences often give a varied physiognomy 

 to xerophilous formations ; they are however only 

 quantitative and not qualitative, for every natural com- 

 munity of xerophytes includes the most diverse types 

 intermingled in various proportions. For instance, in 

 one locality succulent plants predominate, in another 

 thorny shrubs with pinnate leaves, in still another 

 sclerophyllous or very hairy plants ; other forms are 

 however always present as auxiliary species. 



iii. HYGROPHYTES. 



Wiesner ] cultivated in absolutely saturated air a 

 number of plants of more or less decided xerophilous 

 character, especially some which naturally possess basal 

 rosettes of leaves, and, leaving out of consideration 

 those plants that became diseased, he obtained es- 

 sential deviations from the normal structure. The 

 leaves attained extraordinary dimensions, the rosettes 

 by lengthening their internodes became converted into 

 long shoots (Fig. 21)- Under similar conditions in 

 Lothelier's experiments, slightly foliaged or non-foliaged 

 thorny xerophytes were converted into absolutely or 

 nearly thornless plants with abundant foliage (Fig. 22). 

 Xerophytes when cultivated in very moist air, provided 

 they can endure it, acquire a quite abnormal structure 

 which app roadies that of hydrophytes. 



Typical hygrophytes have xveakly developed roots, 

 elongated axes, and large thin leaf-blades. They are 

 hardly ever thorny, as the parts of their vegetative 

 shoots always assume the form of foliaged shoots and 

 of leaves ; they may, however, be prickly, as prickles 



1 Wiesner, III. 



SCH1MPER C 



Fig. 21. 

 Taraxacum of- 

 ficinale. .Left 

 hand : leaf, in 

 nature about 6o 

 cm. long, in ab- 

 solutely satu- 

 rated air. Right 

 hand : leaf, in 

 nature 1 2-1 5cm. 

 long, from a mo- 

 derately damp 

 locality. After 

 Wiesner. 



