ANNOTATIONS AND ADDITIONS. 125 



organic life. But is the number of organic forms itself a 

 constant number ? Do new vegetable forms spring from 

 the ground after long periods of time, while others become 

 more and more rare, and at last disappear ? Geology, by 

 means of her historical monuments of ancient terrestrial 

 life, answers to the latter portion of this question affirma- 

 tively. " In the Ancient World," to use the remark of an 

 eminent naturalist, Link (Abhandl. der Akad. der Wiss. 

 zu Berlin aus dem Jahr 1846, S. 322), "we see characters, 

 now apparently remote and widely separated from each 

 other, associated or crowded together in wondrous forms, as 

 if a greater development and separation awaited a later age 

 in the history of our planet " 



( 14 ) p. 19. " If the height of the aerial ocean and 

 its pressure have not always been the same" 



The pressure of the atmosphere has a decided influence 

 on the form and life of plants. From the abundance and 

 importance of their leafy organs provided with porous 

 openings, plants live principally in and through their 

 surfaces; and hence their dependence on the surround- 

 ing medium. Animals are dependent rather on in- 

 ternal impulses and stimuli; they originate and main- 

 tain their own temperature, and, by means of muscular 

 movement, their own electric currents, and the chemical 

 vital processes which depend on and react upon those 

 currents, zY species of skin-respiration is an active and 

 important vital function in plants, and this respiration, in 

 so far as it consists in evaporation, inhalation, and exhala- 



