PLANT INDUSTRIES 815 
animal enemies that the plant may encounter in its new grow- 
ing place. Thus when corn, which naturally thrives best as 
a tropical or sub-tropical plant, is grown in the north central 
states, the shortness of the season may not allow time for 
ripening the ear; but by experimentation certain varieties of 
corn have been discovered or developed (see chapter on Plant 
Breeding) in which the plant is not so large as the average, 
and the ear, though somewhat smaller, matures in less time. 
Some kinds of seed corn are advertised by the salesmen as 
“ninety-day corn,” which means that the plant will grow and 
ripen a new ear within ninety days, while in case of some 
other varieties of corn more than double that time is required 
for it to mature. Furthermore, in the case of wheat some 
varieties are much less readily affected by the rust diseases 
than are other varieties; some thrive best in certain regions 
when planted in the late autumn (winter wheat); and others 
in other regions thrive best when planted in early spring 
(spring wheat). Every civilized or even partially civilized 
nation depends largely upon one or more of the cereals, and 
in spite of the fact that the nations have been dependent upon 
them for so long, the practices relative to selection of seed, 
cultivation, prevention of diseases, and utilization of the prod- 
ucts have changed very little from decade to decade. The 
application of scientific principles to the production of cereals 
has already shown great possibilities of improvement in plant 
production, but only the most intelligent agriculturists utilize 
these investigations, the traditional “ practices of the fathers ~ 
often dominating the majority of those who till the soil. No 
doubt the decades immediately to follow will bring much new 
scientific knowledge about the growth of cereal crops, and 
nothing seems more fundamental than the application of those 
sciences which may lead to a more effective production of the 
world’s food supply. 
298. Horticulture. Fruits and berries have constituted a 
considerable part of the food of men throughout the period 
covered by history. Wild apples, grapes, and berries, in nearly 
