032 BOTANY OF CROP PLANTS 



There are a number of native species of Lactuca in this 

 country. Britton and lirown mention eight species native 

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

 duced L. scariola. This hitter species is commonly known 

 as the "compass plant." 



Fu;. 259. — Salsify (Tragopogon porrifolius). From left to right: unopcr. 

 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 nui}' be tlis- 

 tinguished by the following artificial key: 

 Kl:y to Tyl>i:s of Li:TTi;cii 

 Basal IcaN'cs narrow, distinctly lanceolate, L. saliva \ar. anguslana (asparagus 



lettuce). 



