14 



BULLETIN 289, U. S. DEPARTMENT OF AGRICULTURE. 



mary of the same table. The 25 plants listed separately were selected 

 to represent all the plants upon which this experiment had been 

 conducted in 1911 and 1912. While the average results shown by 

 the selected plants vary somewhat from the results of all the plants, 

 still they are representative of the plants as a whole. It will be noted 

 that the seed production of the uncovered heads varies considerably 

 on the same plant, so that final results must be taken from the average 

 of treated heads on a number of plants rather than on a few plants. 

 For this reason the results given in the summary more nearly represent 

 true conditions than those given in the first part of Table II. 



From the results obtained on the heads not covered with tarlatan 

 it will be seen that artificial manipulation was detrimental to seed 

 production, since the average yield of the check is higher than that 



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F IG> 4.— Heads of red clover covered with tarlatan to prevent pollination by insects. 



of any treated series. This is undoubtedly due to the fact that the 

 flowers were somewhat mutilated during the operation. Very little 

 seed was obtained from the heads which were kept under cover and 

 artificially manipulated. The few seeds obtained were probably the 

 result of cross-pollination by bumblebees when the tarlatan cloth had 

 been pushed against the heads by rain or had been cut by grass- 

 hoppers. Rains would wash the starch from the tarlatan, thus per- 

 mitting it to fall against the clover heads and allowing the flowers to 

 protrude. This was avoided by either straightening out the cloth 

 after it had dried or re-covering the heads. A few flowers on some 

 heads, however, were exposed to the action of insects for a very 

 short time. In the work which was conducted at Altoona, Iowa 

 the grasshoppers were so bad that some heads had to be re-covered 



