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TEXTBOOK OF BOTANY 



ance. When they are slender, elongate cylinders, such as those of grasses, 

 they are called fibrous roots. If the primary root continues its downward 

 course and becomes the principal large root of a plant, it is often called 

 a taproot. Sugar beet, mullein, sunflower, pigweed, walnut, hickory, 

 alfalfa, and red clover have taproots. Taproots are of two types, woodv 

 and herbaceous, with many gradations between. Those of hickory and 

 walnut are woodv. Those of beets, long conical radishes, dahlias, and 

 sweet potatoes are usually herbaceous and greatly thickened. Thev are 

 composed mainly of parenchyma cells with relatively few woody cells. 

 Such thickened herbaceous roots are often referred to as fleshy roots. 



The beets and radishes of commerce are not entirely roots. The upper 

 part of each one consists of a thickened hypocotyl and the short stem to 

 which the rosette of leaves was attached (Fig. 114). The edible part 

 of some varieties of globe radishes is almost entirely thickened hypocotyl. 



COTYLEDONS 



Fig. 114. Globe radishes develop primarily from the hypocotyl of the seedling. 



