INVESTIGATIONS SINCE MENDEL 



555 



of the plant or animal whose cell is dividing organizes separatdy 

 into chromosomes, thus one-half of the number of chromosomes 

 being composed of father chromatin and the other half being com- 

 posed of mother chromatin. This means that the chromosomes 

 contributed to the offspring by each of the parents maintain 

 their individuality in the offspring. In vegetative cell division 

 each chromosome splits longitudinally, and to each new nucleus 

 there is contributed a half of each chromosome. It is obvious 





Fig. 482. — A diagram illustrating the behavior of chromatin in the reduc- 

 tion division. For convenience the chromatin contributed by the father of 

 the plant, the division of whose cell the diagram illustrates, is shown black 

 and the chromatin contributed by the mother plant is shown white. In the 

 upper line, organization of the chromosomes and their pairing, each pair con- 

 sisting of one father and one mother chromosome; in the lower line, the dis- 

 tribution of the chromosomes in the formation of the daughter nuclei. In 

 this case one of the daughter nuclei receives one father and three mother 

 chromosomes, while the other daughter nucleus receives one mother and three 

 father chromosomes, but this is only one of a number of ways of distributing 

 the chromosomes. 



that the vegetative cell division tends to distribute the chromatin 

 from both parents equally to the new nuclei. But in the reduc- 

 tion division, as shown in Figure 4^2, whole chromosomes and 

 not halves are contributed to each new nucleus, and conse- 

 quently the new nuclei resulting from the reduction division 

 receive only half as many chromosomes as the mother cell con- 

 tained. In the reduction division the chromosomes contributed 

 to the daughter nuclei may be only those of the mother parent or 

 only those of the father parent, in which case the daughter nuclei 



