10 



BULLETIN 75, U, S. DEPARTMENT OF AGRICULTURE. 



RELATION OF TRIPPING TO THE DEVELOPMENT OF SEED. 



In order to obtain more abundant data in regard to the relation 

 of tripping to the production of pods and seeds, the experiment here 

 described was conducted: 



On selected plants, approximately two-thirds of the branches were 

 inclosed in fine-meshed mosquito-bar tents to prevent insects from 

 having access to the flowers. Tarlatan was the material used for 

 the netting. The meshes averaged 25 to the linear inch, thus being 

 from one-half to one-third finer meshed than ordinary mosquito 

 bar, which was thought to be too coarse to exclude the smaller insects 

 which might gain access. The remaining stems of each plant were 

 left outside the tent, where the flowers could develop under natural 

 conditions. On both portions of the plant a number of racemes were 

 marked, each with a tag, and numbered. All unopened flower buds 

 and aU wilted or tripped flowers were cut off from each of these 

 racemes, leaving only the fresh, open, and untripped flowers. The 

 flowers on approximately one-haK of the marked racemes inside the 

 netting were artificially tripped. This was done usually by means of 

 a slender alfalfa stem or grass stem, pushed down between the keel 

 and the standard. On some of the plants used in this experiment, a 

 separate stem was used for each flower, so as to exclude poUen from 

 other flowers, while on other plants the same stem was used to trip 

 several flowers on the same plant. The flowers were f ertiUzed in aU 

 cases, therefore, with pollen from the same flower or with pollen of 

 other flowers on the same plant. The flowers on the remaining 

 racemes inside of the netting tent were allowed to develop without 

 being tripped through the visit of insects or by any artificial agency. 



This experiment was carried out at Pullman, Wash., in 1908, 1909, 

 and 1910; at Chico, Cal., in 1908 and 1909; at Arlington farm, Vir- 

 ginia, in 1908; at Chinook and Havre, Mont., in 1909; and at New 

 London, Ohio, in 1912. The summarized results are shown in 

 Table 11. 



Table II. — Pods and seeds producedby alfalfa flowers on the savie plants, free and pro- 

 tected from insects. 



A. — Outside Ketting: Flowers Developed under Natural Conditions. 



Year. 



Place. 



Number 

 of plants. 



Total 

 number 



of 

 flowers. 



Number 

 of pods. 



Total 

 number 



of 

 seeds. 



Flowers 

 bearing 

 pods. 



Average 

 number 

 of seeds 

 per pod. 



190S 



Piinmnn , , 



7 



15 



1 



15 



10 



9 



8 



6 



633 



3,474 



80 



1,468 



944 



366 



1,589 



228 



157 



155 

 321 



35 

 480 

 143 



51 

 228 



30 



56 



420 



681 



31 



1,730 



320 



Per cent. 

 24.47 

 9.24 

 43.75 

 32.69 



15. 14 

 13. 93 

 14.34 



13. 15 

 35. 66 



2.74 





Chico 



2.12 





Arlington 



.88 



1909 



Pullman 



3.60 





Chinook 



2.23 











Chico 







1910 



Pullman . . 



38 

 105 



1.26 



1912 



New London 



1.80 







Total 



77 



K,9:<!) l.VM 



3,331 







Average 





16.76 



2.22 















