2 PRINCIPLES OF PLANT-TEEATOLOGY. 



" cones " of G-ymnosperms and Vascular Cryptogams, 

 and the sporophylls of Ferns, which are not contained 

 in what we usually term a " flower." 



I. DIFFERENTIATION. 



The simplification, referred to above, which has 

 occurred during the process of the evolution of the 

 flower, will tend to be counteracted from time to time 

 by abnormal breaks in the direct line of progress, taking 

 the form of less simple and more highly differentiated 

 structures, some of which may, with a fair amount of 

 certainty, be attributed to reversionary tendencies on 

 their part — harkings-back, under the influence of this 

 or that stimulus (the nature of which may, or may not, 

 be discoverable), to conditions of greater complexity 

 obtaining in the ancestry of the plants affected. 



1. PROLIFERATION. 



This phenomenon consists in an extension of the 

 axis beyond its normal limits. It may assume various 

 forms according to its degree of development or the 

 nature of the appendages which it bears. There may 

 be either an unbranched median extension of the axis; 

 or there maybe axillary branching without any abnormal 

 extension of the main axis; or both phenomena maybe 

 combined. 



A discussion of the subject will be entered upon 

 a,fter instances of the various types have been cited. 



Median Peoliferation. 



1. The Inflorescence. — This may be either repro- 

 ductive or vegetative in character. 



As an instance of the former may be cited the case 

 mentioned in the ' Grardeners' Chronicle ' of 1881 of a 

 female cone of the Norfolk Island pine {Araucaria 

 eKxelsa) the axis of which extended upwards and 



