ALFALFA 



347 



Isolated plants of alfalfa produce most seed. West- 

 gate compared isolated plants vegetatively propagated 

 from the same mother plant. The plants that were 

 farthest apart namely, 18 by 39 inches produced 

 as many as 505 pods each, while those closest together 

 namely, 7 inches each way produced a maximum 

 of but 38 pods. The beneficial effect of isolation seems 

 partly due to the increased sunlight 

 received, as shaded plants produce but 

 few pods. It is possible, too, that the 

 heat of the sun favors tripping, as flowers 

 can be tripped with a burning glass or 

 by shading under a cage and then ex- 

 posing to the hot sunshine. 



Abundant moisture lessens seed pro- 

 duction, apparently mainly because it 

 stimulates the growth of new sprouts. 

 Too little moisture may also seriously 

 reduce the seed yield, but alfalfa with 

 its deep root system is not frequently 

 subjected to this extreme. The subject FIG. 35. A well- 

 is a difficult one for field experimenta- set duster of alfalfa 

 tion, but needs much further study. 



Tripping of the flowers (Par. 413) is doubtless an impor- 

 tant factor, but more data and observations are needed, es- 

 pecially with reference to the relation of climatic factors 

 to tripping. The relative importance of automatic 

 tripping and insect tripping remains to be ascertained, 

 but observations indicate that in some localities when 

 tripping insects are rare, automatic tripping is probably 

 the determining factor. 



In all producing sections, the yield of seed varies 

 greatly from season to season, but the factors actually 



