624 



THE STRUCTURE OF ECONOMIC PLANTS 



to erect. The leaves vary in color from light to dark green; 

 and, in some forms, this is modified by a reddish or brown pigment. 

 This accessory pigment may be light, medium, or dark in intensity 

 and is a sufficiently constant character to be used in the descrip- 

 tions of commercial varieties. 



Cabbage varieties, known as butter heads, are so called because 

 of their flavor and the oily appearance of the inner leaves, which 



ifsseftr-f^^r* '^ ■ 



Fig. 314. Field of lettuce in head, variety New York. (Courtesy of the Ferry Morse 



Seed Co.) 



are thick and soft in texture with entire margins. The leaves 

 of the crisp or curled cabbage types are brittle with conspicuous 

 veins and margins that are crinkled or curled. Non-heading or 

 bunching varieties may have leaves of either the butter or the 

 crisp type. In cut-leafed lettuce, the loosely spreading leaves are 

 6 to 10 inches long and deeply incised on the edges. The Cos 

 variety has spatulate leaves that are long and entire or sometimes 

 sparingly dentate. They are upright in habit of growth and form 



