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A TEXTBOOK OF THEORETICAL BOTANY 



Carex shows dimorphism, the thick primary roots being hairless and the 

 finer secondary branches hairy. 



A number of Monocotyledons, for example Elodea, Potamogeton and 

 Carex, develop special hair-producing cells or trichoblasts, which remain 

 short while the rest elongate, and only from these short cells are hairs formed. 



Fig. 794. — Stages in the development of a typical root hair from a cell of the 



piliferous layer. 



The formation of these short trichoblasts is an example of the rare pheno- 

 menon of unequal cell division. Most plants, however, develop hairs from 

 the majority of the superficial cells, the proportion varying between 60 and 

 100 per cent., even in the same species under uniform conditions. A few 

 species have the habit of forming hairy regions in successive zones, but 

 normally hair formation is continuous. 



Each hair consists typically of an unbranched cylindrical tube in open 

 connection with its basal cell (Fig. 794). There is a thin lining of cytoplasm 



