14 CIRCULAR NO. 124, BUREAU OF PLANT INDUSTRY. 



In cases where the ear-bearing phmt i)ro(luced two ears it was 

 hoped that tlie effect of cross-pollination might be measured by pure 

 seeding one of the ears and using foreign ]x)llen on the other. In this 

 way it might.be possible to determine the effects of crossing two 

 varieties witli seed of the same color. But the normal range of varia- 

 tion in the size of seed between the first and second ears of the same 

 plant when both were pure seeded was found to l)e so large as to 

 obscure any differences that might be expected from the use of foreign 



pollen. 



^ NATURE OF THE INCREASE. 



The Chinese variety in which the phenomenon of increased size 

 was first noticed has very small seeds, suggestmg that the increase 

 that followed cross mg should be looked upon as the immediate 

 inheritance of larger seed of the jiollen parent. The other alternative 

 is to consider the increased size of the seed as connected with the 

 greater vigor so frequently shown m the first generation of a cross. 



Roberts ' finds difficulty upon morphological grounds in admitting 

 the possibility of this second view. He holds that the growth stimu- 

 lus of the pericarp must be inherited from one of the parents and that 

 additional growth that resulted from a mere increase of vigor would 

 produce an endosperm too large for the pericarp. 



In the experiments here reported there is no evident relation 

 between the size of seed in the pollen-prod ucmg variety and the 

 amount of increase resulting from cross-pollmation. In fact, the 

 greatest increase was secured by poUmatrng with a small-seeded 

 variety, and there is one instance (plant No. 219) where an mcrease 

 in the size of the seed of the large-seeded Hickory King variety was 

 secured by pollhiating with a variety whose seetJs weighed only half 

 as much as those of the Hickory King. It may be necessary to con- 

 clude that the growth of the })ericarp is stimulated du-ectly by the 

 growth of the endosperm. In experiments thus far reported, how- 

 ever, the necessary increase in the size of the jiericar]) would be com- 

 })aratively slight and to seek any explanation may ])e superfluous. 

 An increase of 22 per cent in the volume of a seed, which is the 

 largest reported, would require an increase in the superficial area of 

 the pericarp of only about 2.8 per cent. 



If an increase of from 2 to 20 per cent in the weight of the seed 

 can be secured through the stimulation of foreign ])ollen, the fact is 

 of more than scientific interest. Direct e%ddence that important 

 increases can be secured by allowing two varieties of the same color 

 to cross-pollinate has been given Ly Carrier,- who secured yields of 



1 Roberts, H. F. 



2 Carrier, Lyraaii. Loc. cit. "reventing cross-pollination of corn by means of miLslin screens. Paper 

 read before the American Society of Agronomy, Washington, D. C, Nov. 14, 191'>. 



[Cir. 124] 



