632 BOTANY OF CROP PLANTS 



There are a number of native species of Lactuca in this 

 country. Britten and Brown mention eight species native 

 of the eastern and northern United States, besides the intro- 

 duced L. scariola. This latter species is commonly known 

 as the "compass plant." 



Fig. 259. — Salsify (Tragopogon porrif olius) . From left to right: unopen 

 flower head; side view and face view of open flower head ; achene with pappus at 

 tip of beak. 



Types of Lettuce. — Four types or botanical varieties of 

 cultivated lettuce are recognized. These may be dis- 

 tinguished by the following artificial key: 

 Key to Types of Lettuce 

 Basal leaves narrow, distinctly lanceolate, L. saliva var. angustana (asparagus 



lettuce). 



