190 GENERAL BOTANY 



parental characters ($, F, w, #). If we accept Mendel's conclu- 

 sions as to the stability of plant characters and their separation 

 in the germ cells, we can understand the above four classes of 

 grandchildren. In Fig. 100 the various possible combinations 

 of the characters $, F, w, g, as they might occur in the male 

 and female gametes of the children (Fig. 99), are shown above 

 and at the left of the large square. In the small squares the 

 possible combinations of these characters in the zygotes (grand- 

 children) are illustrated ; assuming that wherever S or Y occur 

 they would dominate w and g, the four classes of grandchildren 

 would appear in the ratio indicated by the small circles, repre- 

 senting peas, in the small squares. These ratios are shown in 

 Figs. 99 and 100 to be 9 SY to 3 Sg to 3 wY to 1 wg. According 

 to the above experiments the characters of plants seem to be 

 represented by factors in the germ cells which are capable of 

 reproducing parental characters in the offspring resulting from 

 a cross. When plants are crossed, these factors are reshuffled 

 and appear in different combinations in the offspring. It has 

 already been shown by experimental breeders that the great 

 variety manifested by plants and animals, as regards color, form, 

 and structure, is due in many instances to these chance Mende- 

 lian combinations in hybrids. It is not possible at the present 

 time to state how universally Mendel's principles will apply to 

 the behavior of plant and animal characters in hybrids and their 

 offspring. Enough has been done, however, to indicate the great 

 value of his results in placing animal and plant breeding upon 

 a more accurate scientific basis. 



Practical applications. The results of Mendel's work which are 

 most. important to the plant breeder are as follows: First, the 

 breeder may find out by observation and experiment the various 

 desirable and undesirable characters of plants which he wishes 

 to cross. Second, he is certain that the desirable characters will 

 not be contaminated or lost in crossing, although they may 

 appear to be so in the children of the first parents. Third, he 

 knows also that by proper care in self -fertilizing children of the 

 first cross the characters of the original parents will reappear in 

 all possible combinations in the grandchildren and their progeny 



