296 



INTRODUCTION TO CYTOLOGY 



of his work on Abies balsamea. According to Hutchinson (Fig. 121) 

 there appear in the fusion nucleus two groups of chromosomes, each 

 containing the haploid number (16). A spindle is differentiated about 

 each group; and the two spindles soon unite to form one, thus bringing 

 the two chromosome groups, representing the two parental contributions, 

 into closer association. The chromosomes now approximate two by two 

 to form 16 pairs. The members of each pair twist about each other and 

 become looped; each of them becomes transversely segmented at the 

 apex of the loop, forming 32 (2x) pairs of segments; these pairs separate 

 to form 64 (4x) chromosomes; a new spindle is formed and 32 (2x) 

 chromosomes pass to each pole. 



ABk £5 



I* • •«•) 



FUSION 



NVCklUt 



TWISTING I OOPinC. 



SttMfcltTflTION 



HX StontNTS 



fIRST TWO 

 CnSBTO NUCLII 



(i* • it.) 



If. TO torn TOLl 



jT IG< 12 i. — The behavior of the chromosomes in fertilization and the first embryonal mitosis 



in Abies, according to Hutchinson. (1915.) 



This interpretation of chromosome behavior at fertilization is remark- 

 able not only because it indicates features resembling those of the hetero- 

 typic prophase, but chiefly because it actually calls for a qualitative 

 reduction of the chromatin at the first embryonal mitosis if the chroma- 

 tin is not qualitatively the same throughout the nucleus. This impli- 

 cation has not been discussed by the advocates of the new theory. The 

 chromosomes pair and twist about one another in a way that parallels 

 closely their behavior during the prophase of a reduction division. That 

 the doubleness seen is due to a pairing and not to a splitting as has 

 heretofore been held is supported by the assertion that the pairs are 

 present in the haploid number, rather than in the diploid number as 

 would be the case were a splitting of all the chromosomes occurring. If 

 the two members of each pair were to separate at the first embryonal 



