178 BOTANY 



telephasic chromosomes of Vicia and Tradescantia, which enlarge 

 and coalesce to form a more or less continuous achromatic matrix. 

 This process involves the assumption of a reticulate form of the 

 chromatic karyotin. 



Another view of the matter is the so-called chromonema hypo- 

 thesis. Bonnevie, one of the principal supporters of this theory, 

 considered that each chromosome at telophase differentiates 

 into an endogenous spiral thread, which persists through inter- 

 phase and emerges from the chromosomes at the following pro- 

 phase as a slender filament which later splits. On this view the 

 achromatic material is not continuous from one nuclear generation 

 to another, but is differentiated anew at each telophase as the 

 spiral develops and the term " chromonema " is given to the spiral 

 filament. The achromatic portion swells and becomes the karyo- 

 lymph, at the periphery of which, the nuclear membrane is laid 

 down, while the spiral filament or chromonema persists as a definite 

 structure throughout most or all of the nuclear cycle, and is not a 

 temporary structure concerned with the split at prophase of mitosis. 



This view has been further extended by Kaufmann, working 

 with Tradescantia pilosa. He found that at anaphase in the 

 nuclei of this species, the chromosome is made up of two morpho- 

 logically dissimilar substances, achromatic and chromatic. The 

 chromatic portion occurs as a pair of unbroken intertwined spiral 

 threads, whereas the achromatic portion serves as a matrix for 

 the chromatic material. At the inception of telophase, the achro- 

 matic material becomes continuous with the nuclear sap and the 

 chromatic part of the chromosome maintains the genetic continuity 

 of the chromosome. At early prophase the chromonemata (spiral 

 portions) can be seen as a single thread spirally coiled, or as distinct 

 intertwined threads. With the further onset of prophase, chromo- 

 mere-like swellings make their appearance on the thread, and 

 each of these forms a centre of activity in the formation of new 

 chromonemata. At metaphase, when the chromosomes reach the 

 equator of the spindle, each individual chromosome can be seen 

 to consist of spiral parallel threads showing both chromatic and 

 achromatic material, the former being clearly seen as a pair of 

 spiral threads which become particularly clear at anaphase. 



