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PLANT MORPHOLOGY 



irregular in size and arrangement. Thus the two zones differ both in 

 position and mode of growth. Surface growth predominates in the 

 tunica, while volume growth is characteristic of the corpus. Frequently 

 these zones are not clearly marked off from each other and vary consider- 



1 



Fig. 313. Median longitudinal section of the stem tip of Coleus blumei, X200. In the 

 center is the apical meristem (a) with a leaf primordium (b) on either side. In the axil 

 of each of the older leaves (c) is a lateral meristem (d) that will produce an axillary bud. 



ably in form and relative extent. Moreover, the relative contributions 

 of the tunica and corpus to the three regions of the mature stem are 

 usually difficult to determine and differ according to the species. 



Mature Stem. As in the leaf, the epidermis of the young stem becomes 

 cutinized and contains many stomata. The cortex consists mainly of 

 green parenchyma, but sclerenchyma may be differentiated as develop- 

 ment proceeds. In some stems a well-marked endodermis is present, but 

 generally this layer is not clearly differentiated.. In stems that increase 



