THE REDUCTIOX OF THE CHR0M0S0M1 



231 



Nearly all of the accounts of reduction now appearing, especially tho 

 given by botanists, conform in general to one or the other of these two 

 schemes, though they vary greatly in detail. Both theories have been 

 upheld by competent observers, and it may be possible thai both modes 

 of reduction actually occur; but the same objects have been so differently 

 described by the two opposing schools that it seems very probable thai 

 interpretation is chiefly responsible for the persistent diversity of opinion. 

 For convenience the two theories will be referred to aa Schenu A and 

 Scheme B. 



REST 



SYNIZESIS 



PACHYNEMA 



LtPTONEMA 



STBEPSINEMA 



ZYCONEMA 



ClAKIMCSIS 



MCTEHOT-rni mioiu 



nanoT^nc mitosis 



Fig. 83. — The method of chromosome reduction according t<> 9W 1. 



Explanation in text. 



Scheme A. — The first of the two main interpretations of reduction 

 came into prominence in 1900 and shortly after, when von Winiwarl 

 (1900), Gregoire (1904, 1907, 1909), A. and K. E. Schreiner (1904 L908 . 

 and Berghs (1904, 1905) applied it to the phenomena observed by them 

 in several animals and plants. It- essential points are a- follows Figs. 



83-88) : 



At the beginning of the heterotypic prophase the nuclear reticulum, 

 without breaking down into such distinct elementary aets or alveolar 

 units as are seen in the somatic prophase, take- the form of long slender 

 threads (leptothic or leptonema stage). 1 During the very early prophi 



1 The terms Uptotene, synaptene, pachytene, and <liplot*,< were proposed by von 

 Winiwarter (1900); leptonema, zygotene, pachynema, and stre] bj Gregoire 



(1907); amphitene by Janssens (1905 ; itrepsUene by Dixon I""" : d tis by 



Haecker (1897) ; synapsis by Moore L896 ; . b] McC ing 1906 ;andf* 



by Fanner and Moore (1905). The terms ending in -/.'/.< arc ordinarily used as 

 adjectives. 



