230 



PRINCIPLES OF PLANT-TERATOLOGY. 



regards their essential conformation and structure or 

 their phyllotaxis. 



If this view is incorrect, how are the various 

 abnormal changes from opposite to spiral phyllotaxis to 

 be explained ? They would seem to be meaningless. 

 If, however, it be correct, then these changes are easily 

 explicable as reversions to the primitive type, as 

 eruptions from the rigid groove into which evolution 

 has led the type. The opposite-decussate type of phyllo- 

 taxis is merely a modification of the spiral § type. 

 Baillon observed in a plant of Chimonanthus fra grans 

 that the f leaf-arrangement prevailed throughout the 

 vegetative axis ; as the opposite-decussate type is 

 characteristic of the Calycanthacese this isolated excep- 

 tion is not likely to .be a progressive, but rather a 

 reversionary phenomenon. The four cortical bundles 

 of the vegetative stem of plants of this order are an 

 indication of the opposite-decussate leaf-arrangement ; 

 in the plant of Ghimonantkus seen by Baillon there 

 were five cortical bundles. Now it is interesting that 

 in the peduncle of both Calyranthus and Chimonanthus 

 there are six to eight cortical bundles arranged in 

 five sets (i. e. at two points the bundles are in pairs). 

 As the presence of five bundles indicates the completed 

 transition from the opposite to the f- spiral phyllotaxis; 

 so the presence of the extra number shows the gradual 

 transition to a more complicated arrangement which 

 obtains at a higher level, viz., on the floral axis, and is 

 therefore the more primitive type. 



The leaf-arrangement in the vegetative stem in plants 

 generally is apparently the result of the mean of two 

 distinct kinds of influence, viz., that emanating from 

 above, representative of the more primitive t3qje, and 

 that coming from below in the cotyledonary region. 

 The former influence makes for spiral, the latter for 

 opposite phyllotaxis. In many Dicotyledons whose 

 phyllotaxy is typically alternate the first few nodes 

 have each a pair of opposite leaves, being formed in 

 correlation with the cotyledonary node. In many 



