CHAPTER IX 

 ENVIRONMENT AND LEAF DEVELOPMENT 



Development of a leaf begins with the terminal growth of a primordium. 

 This terminal growth in a fern leaf may continue long after the base of 

 the leaf is mature. The tender, young coiled tip of a growing Boston 

 fern leaf is familiar to all. In the broad leaves of common trees and 

 shrubs all parts of the blade continue to grow and mature about the 

 same time, though growth continues longest in the base. In the leaves of 

 grasses, iris, aloe, and pine the basal region remains meristematic much 



Fig. 37. Growing regions of leaf blades indicated by stippling. The fern leaf 

 (A) continuous growth longest at the apex, and grass leaves (B) longest at the 

 base. The growth of leaves similar to those of the sunflower (C) is much less 

 localized. 



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