CHAPTER XXIV 
PLANT BREEDING 
Plant breeding has to do with the improvement of old plants 
and the securing of new ones. Many and various are the aims 
of plant breeding. The object may be to improve the yield, 
increase the resistance to drought or disease, shorten the period 
of development, or secure strains or varieties with new chara- 
ters. The two important methods used are selection and hy- 
bridization. 
In connection with plant breeding, the discoveries of DeVries 
and Mendel have proven to be of inestimable value. The dis- 
coveries of De Vries have resulted in a better understanding 
of the nature of variations and has enabled us to improve plants 
by selection much more efficiently. The introduction of Men- 
del’s methods of investigation and his discoveries concerning 
the behavior of characters in hybrid offspring afford a scientific 
foundation to the improvement of plants by hybridization. As 
a result of Mendel’s contributions, we now know much more 
about how to proceed, what to expect, and how to interpret the 
results obtained in hybridizing. 
Selection. — Selection takes advantage of variations. Vari- 
ations, as previously noted, are not only due to differences in 
gametes and their combinations in fertilization, but also to 
differences in temperature, moisture, soil conditions, and.other 
environmental factors. But only those variations due to factors 
which can be transmitted by the gametes are inheritable through 
the seed. A Corn plant may be larger or bear larger ears than 
the ordinary type because of especially favorable conditions. 
It may stand alone in the hill, thus having all of the water and 
mineral supply to itself, or it may be growing on ground more 
heavily fertilized. This increased size, due to external condi- 
tions and not to any special factors in the cells of the plant, 
is not transmitted to the offspring, and the embryos in the 
kernels of this especially favored plant may have inherited no 
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