228 A TEXTBOOK OF GENERAL BOTANY 
succeeding division. During the organization of a daughter 
nucleus from a group of chromosomes the chromosomes become 
connected by anastomoses. When the chromosomes reappear in 
the succeeding prophase these anastomoses break down and the 
chromosomes are separate except in so far as they may be 
joined together, end to end, in the spireme. Indeed, where cell 
divisions follow each other in rapid succession the spreading out 
of the chromatin during the resting stage may not go far enough 
to obscure the identity of the individual chromosomes. 
In following the process of division we have seen that the 
nuclear membrane, the karyolymph, and the nucleoli disappear 
during division and are formed anew during the organization of 
the daughter nuclei. The chromosomes not only appear to per- 
sist from one cell generation to the next but they are the only 
parts of the nucleus that do so. For this and other reasons they 
are generally regarded as the most important constituents of the 
nucleus and as the site of the mechanism or factors which deter- 
_mine the hereditary characteristics of an organism. 
Chromosomes and fertilization. During the process of fertiliza- 
tion the male nucleus and the egg nucleus come together and the 
sides that meet become flattened against each other. The parts 
of the two nuclear membranes that are in contact disappear, and 
thus the contents of the two nuclei come to be inclosed by a 
single nuclear membrane, a part of which comes from the male 
nucleus and a part from the egg nucleus. In this way the chromo- 
somes which were in the male nucleus are added to those which 
were in the egg nucleus. The fertilized egg thus contains the 
chromosomes of both the egg nucleus and the male nucleus, or, 
usually, double the number of saves sigeite 3 that were in either 
of the fusing nuclei. 
When the fertilized egg nucleus divides, every chromosome 
splits into two, and one of each pair of the resulting chromo- 
somes goes to each daughter nucleus. In this way each daughter 
nucleus contains the same number of chromosomes as the nucleus 
of the fertilized egg. The chromosomes divide in the same man- 
ner in the second and all subsequent nuclear divisions in the 
