196 THE POPULAR SCIENCE MONTHLY 
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Fic. 1. Types APPHARING IN A SINGLE Fip~D or MaizH. A strain like the ear near 
the center has been isolated. 
it simply takes an alert eye for their detection, comparative tests to 
prove their merit and the time needed to produce a sufficient increase 
for commercial use. Some of our other important grain crops like oats 
and rye are more often cross-pollinated, as is also our chief grass crop, 
timothy. But as maize is probably the most difficult crop to deal with, 
and is a typical cross-pollinated plant as well as our most important 
cereal, perhaps it will be of interest to take a short survey of some of 
the problems with which one has to deal when endeavoring to improve 
it by selection. 
Maize is the only one of our cereals that is monecious. The tassel 
contains the pollen or male element while the silks are the stigmas of 
the female flowers. In order that the pollination of the silks shall be 
relatively certain, each tassel produces about thirty million pollen 
grains; and as the ears average less than five hundred seeds apiece, there 
are about sixty thousand pollen grains produced for each kernel. With 
such a large amount of superfluous pollen floating around in the air, 
there is a great deal of inter-crossing between the neighboring plants. 
This fact has been an obstacle to the improvement of maize, but it has 
been offset by one advantage it possesses over the other cereals, that of 
producing large ears. Since each individual ear must be handled and 
its characters noted at husking time, it is not strange that ears with 
desirable variations sufficiently striking to catch the eye of the grower 
have become the parents of numerous distinct varieties. By selecting 
desirable seed ears and isolating them from other varieties, various 
strains have been produced that are remarkably uniform in characters 
such as color that have forcibly attracted the attention of the breeder. 
Even in these strains, however, there are many natural types growing 
side by side and continually crossing with each other. There are stalks 
