138 



INTRODUCTION TO CYTOLOGY 



ments. In any event the arrangement of the chromatic matter in the 

 form of a long, slender, and relatively straight thread during the prophase 

 strongly suggests that it is at this time that it becomes morphologically 

 double, whatever the number of nuclear cycles in advance of the anaphasic 

 separation. Very little can be said at present concerning how or at what 

 stages any smaller elements within the chromonema undergo multiplica- 

 tion. Physiological considerations suggest that this occurs during the 

 interphase or metabolic stage, but adequate evidence is not yet available. 



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Fig. 76. — Somatic mitosis in plants with slender or small chromosomes, a, telophase 

 in Ceratopieris. b, interphase in Pteris. c, prophase in Polypodium. d-h, anaphase, 

 telophase, interphase, early prophase, and late prophase in Azolla. {After de Litardiere, 

 19216.) 



As examples of the appearance of smaller chromosomes in some of the 

 stages of the mitotic cycle may be cited certain cases in ferns described 

 by de Litardiere (19216). In Pteris cretica and other forms with very 

 slender chromosomes, the latter undergo no conspicuous changes in 

 internal structure during the telophase but are drawn out into filaments 

 connected by anastomoses to form the interphasic reticulum. In the 

 prophase the anastomoses disappear and the chromatic substance is 

 concentrated directly into slender threads which soon appear double and 

 thicker (Fig. 76, a to c). In Azolla caroliniana the chromosomes are 

 very small, ovoid bodies. They undergo no obvious change other than 

 the development of anastomoses during the telophase and remain clearly 

 visible through the interphase. In the prophase the anastomoses dis- 

 appear, after which the chromosomes elongate somewhat, become double, 



