OTHER CLASSES OF ADAPTATIONS 433 



are convergent adaptations characteristic of numerous 

 desert plants the world over. Incidentally it may be said 

 that as a result of this adjustment to the environment 

 the agave, represented by such species as the century 

 plant of this country, bears a close resemblance to the 

 old world aloes, and the cactus closely duplicates the 

 African spurges. 



The plants of high mountains and of the treeless re- 

 gions of the far north, where deep snows prevail through- 

 out the greater part of the year, form low dense mats or 

 carpets. Convergent adaptations appear in the case of 

 many species where the over-lapping leaves chiefly rest 

 on the ground and diminish the loss of heat, while the 

 roots are generally loaded with starch and furnish the 

 food necessary for the rapid growth of the plant during 

 the short summer. 



The plants adapted to an existence in water, or to the 

 sandy stretches bordering the sea and the larger lakes, 

 or to any other relatively large territory where essentially 

 the same conditions prevail, possess certain features in 

 common ; but considerations of space prevent their 

 detailed description. 



Other Classes of Adaptations. — While the animals 

 and plants of a given region, or in different districts where 

 the same general conditions prevail, may manifest this 

 convergence or parallelism of form, it is equally true that 

 every species possesses its own particular adaptations 

 which enable it to live amid surroundings more or less 

 different from those of any other species. Indeed it is 

 these minor adaptations which in large measure serve to 

 distinguish one species from another. The relations of 

 plants to their environment are usually less complex than 

 in animals with highly developed nervous systems, sense 

 organs, and active powers of locomotion. Accordingly, 

 plant adaptations are less obvious and not generally so 

 striking as those in the animal kingdom, though they are 

 as universal and belong to the same general classes. 



