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A TEXTBOOK OF THEORETICAL BOTANY 



the young shoot apex continues to form new leaves for a short time in the 

 early part of the year, but this does not continue much beyond the end of 

 May, after which the apex is again transformed into a winter bud (Fig. 973), 

 in which the later formed primordia are retained till the following spring. 



Fig. 973. — Acer pseiiddplataiuis. Longitudinal section of 

 winter bud showing the protective scales and young 

 foliage leaves already formed ready for expansion in the 

 spring. The photograph also shows two smaller 

 axillar\' huds of similar construction. 



Phyllotaxis. 



The placing of the leaves on the shoot, known as phyllotaxis, is ultimately 

 due to the sequence and the spacing of the leaf rudiments, as they appear on 

 the surface of the meristematic apex of the stem, and it involves some of the 

 subtlest and most obscure of the space-time relationships which we have 

 already indicated as fundamental in apical development. Unfortunately 

 the lack of factual knowledge and the facility with which the subject lends 

 itself to geometrical and mathematical deductions, have combined to lead 

 attention away from the living plant and towards a labvrinth of theory, which 



