INTERPRETATION OF PROCESSES OF NUCLEAR DIVISION 219 



beginning with the fertilized egg. When the sperm nucleus 

 fuses with the egg nucleus the number of chromosomes borne 

 by the sperm is added to the number borne by the egg, and the 

 fertilized egg, therefore, bears twice as many chromosomes as 

 does the sperm cell or the unfertilized egg cell. Now while 

 these chromosomes lie closely associated in the fertilized egg 

 they do not commingle and lose their identity; there is, rather, 



o 



D 



Fig. 126. — Showing method of association of paternal and maternal chromosomes, 

 at .4 in all vegetative nuclei, and B, C, D, their manner of separation in all vegetative 

 nuclear divisions. Showing also manner of association of paternal and maternal chromo- 

 somes at E in early prophase of spore grandmother cells and the manner of their separation 

 during the division of the grandmother-cell nucleus at F and G. Showing also the longi- 

 tudinal division of the chromosomes in the spore mother cells in H, and their separation to 

 form the spore nuclei in 1, two of the four spores being purely paternal and two purely 

 maternal. 



evidence for the conception that they become joined by end-to- 

 end contact, as shown in Fig. 126, A, where the black segment 

 represents a paternal and the white a maternal chromosome. 

 For simplicity only one chromosome from each parent is shown. 

 When division of the fertilized egg takes place the chromosomes 

 break apart where they are joined end to end, divide longitudi- 

 nally and line up at the equator, as shown at B; and so longi- 

 tudinal halves of both paternal and maternal chromosomes 

 arrive at either pole, C and D. Throughout all subsequent 

 cell-divisions leading to the mature plant body this method of 

 division is repeated, and each of the myriad cells is thus sup- 



