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- 

 logics which "Wolff indicated in their chief outlines and 

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

 them when we regard the phcenogamic 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 Phaenogam, 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 



