168 FIELD CROPS FOR THE COTTON-BELT 



to find very little data on the growth of corn leaves. That 

 the growing zone of a corn leaf lies at its base is shown by 

 its continued elongation even though the tip of the leaf 

 is cut off. There are, in all probability, two active grow- 

 ing zones in the corn leaf, one being at the base of the leaf- 

 sheath and the other at the base of the blade. , 



REPRODUCTION 



Attention has been called to the fact, page 27, that 

 the production of a new plant does not begin with the 

 germination of the seed. The seed itself is an embryonic 

 plant possessed of a certain food supply and protective 

 coverings. The new individual comes into existence with 

 the formation of the seed as the result of a complex and 

 peculiar physiological process known as fertilization. The 

 organs of reproduction in corn have been discussed in a 

 previous chapter and the process only will be considered 

 here. 



212. Fertilization. In order that fertilization may 

 take place it is necessary that the pollen-grains from the 

 tassel come in contact with the exposed portion of the 

 silk. This transfer of pollen from the tassel to the silk is 

 a mechanical process which takes place through the agency 

 of the wind. It is spoken of as pollination. For complete 

 fertilization to take place, every silk must receive at least 

 one pollen-grain (Fig. 26). , 



Each pollen-grain consists of merely two cells, a smaller 

 cell within a larger. After lodging on the moist surface 

 of the silk the larger cell germinates and sends out a 

 vegetative tube which grows through the entire length of 

 the silk or style, penetrates the ovule and comes in contact 

 with the egg-cell (Fig. 27). The smaller cell of the pollen- 

 grain, which is largely nucleus, divides and one of these 



