122 PLANT-BREEDING 



is the large size of the ears and their enormous number of 

 seeds. 



On a normal individual, the female or pistillate flowers 

 are combined on the ears, and at the time of flowering the 

 pistils or silks are protruded from the top of the husks. The 

 wind has to carry the pollen to them. The male or stam- 

 inate inflorescences are the tassels on the top of the stallcs. 

 Each flower contains three stamens, and each tassel pro- 

 duces about 20,000,000 to 50,000,000 grains of pollen. By 

 far the largest quantity of these is, of course, lost, being depos- 

 ited on the foHage or falhng to the ground. But a sufflcient 

 number are transferred to the silks to insure the complete 

 fertiHzation of the ears. Tliis, however, is not reached at 

 once, but several days are needed for the process. The silks 

 do not all appear at the same time, those of the uppermost 

 kernels being the first. Moreover, they continue growing 

 until a considerable length is reached. The diffusion of 

 the pollen mainly takes place early in the morning, when 

 the scales and anthers open under the influence of the rays 

 of the sun. Four or five days are usually required to pollin- 

 ate all the silks of an car. 



It is evident that only a part of the pollen will fall upon 

 the silks of the same plant. This is called self-polhnation 

 or self-fertilization. The stronger the wind blows, the great- 

 er the quantity that drifts to other ears, thereby insuring 

 cross-fertilization. Pollen will drift in tliis way over long 

 distances, and is known to have been carried by the wind 

 over more than a thousand feet of surface. If kernels of one 

 mother ear are sown close to one another the pollen may be 

 transferred to the children of the same mother, and this is 

 called close-pollination. 



The effects of cross-fertilization often can be seen when 

 different varieties are cultivated on adjacent fields. Some 

 color-varieties and the sweet corns are exceedingly liable to 



