414 



MEMOIRS OF THE AMERICAN ACADEMY. 



far as it affects any useful quality or character. But variation, not only 

 animals, but also in many of the higher plants, is much more limited th 



m 



these causes seem capable of accounting for. It is, apparently, as limited in 

 respect to useless though conspicuous features as in those that are of 

 nized value to life. Sexual Selection, through which the . characters of 



g 



anim 



and 

 any 



are chosen by themselves, or brought into relation to their perceptive and 

 other psychical powers, is the cause assigned for this fact in the case of ani- 

 mals ; that is, forms are chosen for their appearance, or for the pleasure they 

 give to the senses. But plants have no senses, except a sense of touch ; 

 they have no other known psychical powers. Nevertheless they present n 

 conspicuous features of beauty to the eye, and many give forth agreeable and 

 characteristic odors. And such characters are apparently as fixed in many of the 

 higher plants as in animals. The theory of types and the doctrine of Final 

 Causes regard this fixedness and individuality as ends in themselves, or else as 

 existing for the service o[ some higher form of life, or ultimately Jven for the 

 uses of human life. But the theory of the adaptation of every feature in a form 

 of life to its own uses is not without resources for the explanation of these 

 characters in plants ; for though the plant has no sense to appreciate, or power 

 to select, its own features of individuality and beauty, yet the lives of many 

 of the higher plants are essentially dependent on such powers in insects; so 

 that whatever character renders them attractive to insects, or distinguishable by 



their sight, may be said to be of use to plants for the ends of reproduction 



and tends in this way to become a fixed or only slightly variable character. 

 That this cause may have acted not only to determine definite shapes, colors, 

 -d odors m flowers, but also definite features in the foliage of plants, as the 



marks or signs of these, and that the value of such signs may have determined 

 a greater degree of fixedness or constancy in the arrangements, as well as in 

 the shapes of leaves, is an hypothesis that may be added to those we have 

 already considered, concerning the utilities of these arrangements. This cause 

 would tend to g.ve prominence to those features in arrangement which are most 

 conspicuous to the eye, namely, those of cyclic regularity and 

 an explanation of this cyclic character, or the 



ity. S 



of leaves at short 



pie and definite arrang 



lntcrvals ln verticil1 lines on the stem, or the utility of 

 th.. as a chstmguishing charaeter of the plant, is not inconsistent with the 

 physmlog.cal utility in these arrangements, which I have pointed 



two in 



but the 



pointing to the production of the same forms would illustrate a 



