THE MORPHOLOGICAL COMPOSITION OF PLANTS. 69 



in Fig. 122. Or rather, there is everything to facilitate it ; 

 seeing that natural selection will continually favour the pro- 

 duction of a form in which the second frond grows in such 

 way as not to shade the first, and in such way as allows the 

 axis readily to assume a vertical position. 



Thus, then, is interpretable the universal connexion between 

 monocotyledonous germination and endogenous growth ; as 

 well as the similarly- universal connexion between exogenous 

 growth and the development of two or more cotyledons. 

 That it explains these fundamental relations, adds very 

 greatly to the probability of the hypothesis. 



§ 196. While we are in this manner enabled to discern 

 the kinship that exists between the higher vegetal types 

 themselves, as well as between them and the lower types ; we 

 are at the same time supplied with a rationale of those truths 

 which vegetal morphologists have established. Those homo- 

 logies which Wolff indicated in their chief outlines and 

 Goethe followed out in detail, have a new meaning given to 

 them when we regard the phamogamic axis as having been 

 evolved in the way described. Forming the modified con- 

 ception which we are here led to do, respecting the units of 

 which a flowering plant is composed, we are no longer left 

 without an answer to the question — What is an axis ? And 

 we are helped to understand the naturalness of those . cor- 

 respondences which the successive members of each shoot 

 display. Let us glance at the facts from our present stand- 

 point. 



The unit of composition of a Phasnogam, is such portion of 

 a shoot as answers to one of the primordial fronds. This 

 portion is neither one of the foliar appendages nor one of the 

 internodes ; but it consists of a foliar appendage together 

 with the preceding internode, including the axillary bud 

 where this is developed. The parts intercepted by the dotted 

 lines in Fig. 123, constitute such a segment ; and the true 

 homology is between this and any other foliar organ with the 



