1912] CURRENT LITERATURE 447 
the mitotic spindle which have never before been described. These new 
stages are to be found in the prophase immediately preceding the ogee 
of the equatorial plate, and concern the fate of the nuclear membrane. Man 
authors have either described or figured the breaking down of a nuclear 
membrane at a time when the multipolar stage has been reached, or in vege- 
tative cells when the polar caps have been completely formed. Contrary to 
the generally accepted view, LAwson finds that the nuclear membrane does 
not break down or collapse at any period during the spindle development, but 
behaves as one would expect a permeable plasma membrane to behave under 
varying osmotic relations. 
The nucleus is regarded as an wien system, and its membrane consti- 
tutes an essential element in that system. As the prophase proceeds, the 
nucleus or the nuclear vacuole, as he walls it, becomes smaller and smaller, and 
the membrane gradually closes in about the chromosomes, which later become 
crowded together around the nucleolus. When the karyolymph becomes so 
much reduced that it is no longer visible as a clear nuclear sap, the membrane 
becomes — applied to and completely envelops the-surface of each chromo- 
some. consequence, instead of a single osmotic system represented in 
the Sines there have been established now as many independent osmotic 
systems as there are chromosomes. 
The gradual diminution of the nuclear vacuole brings about a condition 
where a limited amount of cytoplasm of reticulate structure is obliged to 
occupy a space which has greatly increased by the reduction in volume of the 
nuclear vacuole. This necessarily sets up in the cell a tension sufficient to 
cause a readjustment and a changed configuration in the reticulate form of the 
cytoplasm, and therefore the cytoplasm in the region of the nuclear wall, 
drawn out from the reticulum by the receding membrane, becomes changed to 
the form of fine threads or fibrils of the “kinoplasm.”” The lines of tension are 
fall back into the reticulate forms, and the setting up of new lines of tension 
by the drawing out of threads from the hitherto undifferentiated reticulum. 
Thus not only individual threads, but entire cones of fi may appear to 
assume different positions. The attachment of the spindle fibrils to chromo- 
somes is brought about by the geen of each chromosome by the receding 
membrane. 
Taking all the stages sbaeved into consideration, the author concludes 
that the achromatic spindle in vascular plants is simply an expression of a 
state of tension in the cytoplasm, and that this tension is caused in the first 
place by nuclear osmotic changes that create a condition where a i 
amount of cytoplasm is obliged to occupy an increased space. 
regards the achromatic figure as not an active factor in mitosis, but sihina 
more than a passive effect of nuclear osmotic changes.—S. YAMANOUCHI. 
