On the Relation of Phyllotaxis to Mechanical 

 Laws. 



By 

 AETHUK H. CHUECH, M.A., D.Sc, 



Lectv/rer in Natural Science, Jesus College, Oxford. 



PAET III. 



SECONDARY GROWTH PHENOMENA. 

 I. Notation. 



In the preceding general survey of the phenomena of Phyllotaxis 

 it has been observed that the arrangement of the lateral members 

 (appendages) of the plant body of higher plant-forms exhibits 

 remarkable phenomena of Rhythm, and the arrangement, that 

 is to say, thus works out as a definite pattern. The exceptions 

 to this generalisation are so few that these may be safely regarded 

 as cases in which the rules have been complicated by further 

 specialisation, or possibly by degeneration in the construction 

 mechanism, and in the vast majority of cases the rhythmic 

 character of the phenomena is their most distinguishing feature. 



In so far as the phenomena are rhythmic, the observed facts 

 admit of mathematical expression ; but at the outset it becomes 

 extremely important to distinguish what exactly are the data 

 afforded by the plant itself, and what conceptions may have been 

 gratuitously introduced into the study of the subject. In the 

 historical development of botanical science it was unavoidable 

 that the first generalisations of plant-morphology should have 

 been founded on the contemplation of adult plant structures, on 

 shoots, for example, which possessed nodes and internodes : a 



p 



