182 



MORPHOLOGICAL DEVELOPMENT. 



It is proper to add that there are some Monocotyledons, 

 as Ravenala madagascariensis, in which this character does 

 not occur. What conditions of existence they are that here 

 hold this natural tendency in check, it is not easy to see.* 



* The Natural History Review for July, 1865, contained an article on 

 the doctrine of morphological composition set forth in the foregoing Chaps. 

 I. to III. In this article, which unites exposition and criticism in a way that 

 is unhappily not common with reviewers, it is suggested that the spiral struc- 

 ture may be caused by natural selection. When this article appeared, the 

 foregoing five pages were standing over in type, as surplus from No. 14, issued 

 in June, 1865. 



