A STUDY IN CHROMOSOME REDUCTION. 621 
that follow one another very rapidly. All of the facts seem to point to the conclusion 
that we have here an accelerated form of merismatic activity, and this acceleration is 
due to the exceptionally high nutritive conditions that prevail. 
gested one other theoretical conclusion, 
namely, that reduction itself represents an accelerated form of merismatic activity. 
That the high state of nutrition generates a physiological condition where two mitoses 
are telescoped into one, as represented in the first meiotic division. ‘These features will 
There were certain features which sug 
be deseribed and discussed more fully in another paper which is now in preparation. 
SUMMARY. 
The conclusions from this investigation may be briefly summarised as follows :— 
There was no evidence found to show that the chromatin ever consists of one 
continuous spireme in the plants studied. On the contrary, there was convincing 
evidence that throughout the prophase there were as many spireme threads as there 
were chromosomes. : 
Hach spireme thread showed a longitudinal fission which appears at a very early 
stage. There was strong evidence tu prove the presence of this fission as early as the 
reticulum stage. 
No “‘synaptic contraction” in its generally accepted sense occurs in the plants 
investigated. The phase of the nucleus known as synapsis is really a growth period, 
during which there is a great enlargement of the nuclear cavity and a withdrawal of 
the nuclear membrane from the chromatin mass. 
Any slight diminution in the volume occupied by the chromatin that may occur 
is due entirely to the shortening and thickening of the chromatic filaments. 
The so-called synaptic contraction is therefore not a feature peculiar to meiosis. 
A similar shortening and thickening of the chromatin threads occurs in all somatic 
mitoses. | 
The spireme threads, which become very much shorter and thicker during the 
prophase, and persistently show a longitudinal fission, are in every way comparable to 
somatic chromosomes. 
Up to the time of reduction, no fundamental difference could be recognised between 
the meiotic prophase and the ordinary somatic prophase. 
Reduction is accomplished by the lateral pairing of somatic chromosomes. 
As this union or pairing is a temporary one, it appears to be a matter of no signifi- — 
cance as to whether the reduction is brought about by an end-to-end or lateral 
conjugation. 
Soon after the bivalent chromosomes are organised, the karyolymph begins to 
exosmose into the cytoplasm, and from this stage on the nuclear vacuole diminishes 
In size. 
The nuclear membrane persists throughout the prophase, and is functional during 
this period in the osmotic transfer of the nuclear fluid into the cytoplasm. 
