186 BOTANICAL GAZETTE [march 



$ 



— Although the actual seg- 



mentation of the chromosomes in Fucus occurs just after the nucleus 

 has emerged from synapsis, their virtual preformation, as continuous 

 chromatin threads from which the chromosomes develop, begins very 

 early in prophase. As was described before, the ragged reticulum 

 of chromatin in the resting nucleus gradually becomes transformed 

 into a thread running in various directions, the transformation being 

 very much more active at the periphery than in the center of the 

 nuclear cavity. The threads in their beginning are uneven and 

 branched, then they become much evener and the transformation 

 continues, so that long continuous threads are formed, running mostly 

 in the peripheral region of the cavity. The threads thus formed 



thread. Moreo\ 



(fig 



from the early beginning of the transformation up to its completion 

 as a continuous structure. Entering into the synaptic condition, the 

 single thread then shortens and thickens, and becomes eccentrically 

 grouped as a loose tangled mass at one side of the nuclear cavity; so 



formed 



of the thread (figs. i8, 20, 43, 44). The loops so developed are there- 

 fore still continuous with one another at the bases where they come 

 in contact with the nuclear wall. The loops then become arranged 

 in a loose bunch, parallel and regular, with their bases attached to 

 the nuclear membrane, while the opposite folds protrude into the 

 cavity. Then the loops continue to shorten and thicken and become 



ated 



has 



that the bent arms are in contact with each other, when synapsis 

 reached its culmination. As they emerge from synapsis (fii-$> 

 there are present 32 bivalent chromosomes, which become detached 

 from the nuclear membrane, moving toward the various regions of 

 the nuclear cavity. 



The relationship of the chromatin thread in prophase, the loops 



clearly followed. 



chromosomes 



be 



chromosomes 



one of the loops in synapsis; the loops being formed by a folding-ba<* 

 of the chromatin thread, so that a loop in synapsis should be con 

 sidered as composed of two sporophytic chromosomes arranged en 



