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The Pairing of the Chromosomes. 
THE PAIRING OF THE CHROMOSOMES. 
HE study of the method of pairing of the paternal and maternal 
chromosomes in meiosis has resolved itself of late years 
mainly into the elucidation of the question whether this union is 
brought about end to end or laterally,—in a telosynaptic or a 
parasynaptic manner. Theoretically it does not seem an affair of 
the first importance which of these processes takes place, nor need 
they be mutually exclusive; indeed it has been shown 1 that both 
may occur simultaneously in the same plant. The evidence, 
however, in favour of an end to end association for the most part 
suggests that this is achieved in the spore mother-cells, whereas 
many of those who have described lateral pairing hold that the 
approximation of homologous chromosomes takes place, not in the 
meiotic prophases but much earlier, so that a spireme, whose double 
character depends on the association of paternal and maternal 
threads, is present in the vegetative divisions. 
A spireme of similar double appearance has been described by 
other observers 2 as due to the longitudinal fission of originally single 
structures, and there seems no doubt that this may be the case 
since a duplicate spireme has been reported in gametophytic nuclei 
where pairing of paternal and maternal elements is obviously 
impossible. 
At the same time the account given of chromosomes which 
have become early associated in pairs is in certain cases exceedingly 
suggestive. Overton 3 for example has described twelve single 
chromosomes in the pollen nuclei of Calycanthus floridus in contrast 
to the twenty-four chromosomes arranged in twelve pairs which he 
finds in the sporophyte. He has observed a corresponding state of 
affairs in other Angiosperms also, and Harper 1 for Phyllactinia has 
described an association so intimate that the two chromosomes 
become an apparently single structure and the distinguishable 
number of chromosomes is unchanged by nuclear fusion. 
1 Digby, “ The Somatic, Premeiotic and Meiotic Nuclear Divisions 
in Galtonia candicans." Ann. Bot., 1910. 
2 Hof, “ Histologisclie Studien an Vegetationspunkt.” Bot. 
Centralbl., 1898. Digby, loc. cit. Fraser and Snell. “The 
Vegetative Divisions in Vicia Faba.” Ann. Bot., 1911. 
3 “On the Organisation of the Nuclei in the Pollen Mother-Cells 
of certain Plants with especial Reference to the Permanence 
of the Chromosomes.” Ann. Bot*., 1909. 
4 “ Sexual Reproduction and the Organisation of the Nucleus in 
certain Mildews.” Publ. Carnegie Inst., Washington, 1905. 
