LEGUMINOS^ 



445 



"automatic" tripping. Humidity and temperature condi- 

 tions are probable causative factors in automatic tripping. 

 Both self- and cross-pollination are effective in alfalfa. 



untrippcd 



lateral ^ 



jfaminal tube- 

 free jfamen 



unfripp 



Fig. 1 88. — Pollination of alfalfa. A, flower untripped with calyx and 

 standard removed; B, same tripped; C, position of staminal tube untripped 

 and tripped. {After U. S. Dept. Agri.) 



Self-pollination usually results from automatic tripping. 

 It is known that good seed crops are produced in regions 

 where tripping insects are scarce. However, the number 



