TRANSACTIONS OF SECTION K. 571 



out the entire prophase the nuclear membrane is functional in this osmotic 

 transfer. As the nuclear vacuole becomes smaller and smaller the membrane 

 gradually closes in about the chromosomes. When the karyolymph becomes 

 so much reduced that it is no longer visible as a clear nuclear sap, the membrane 

 becomes closely applied to, and completely envelops, the surface of each chromo- 

 some. 



For some time previous to the diffusion of the karyolymph the nuclear vacuole 

 occupies a space that may approach or even exceed in size half the volume of 

 the cell-cavity. So that all of these circumstances bring about a condition where 

 a limited amount of cytoplasm of reticulate structure is obliged to occupy a 

 cubical space which has greatly increased by reason of the reduction in the 

 volume of the nuclear vacuole. This necessarily sets up a tension in the cytoplasm 

 — a tension sufficient to cause a readjustment and changed configuration in the 

 reticulate form of the cytoplasm. As the nuclear vacuole becomes smaller and 

 smaller, the cytoplasm in the region of the nuclear membrane becomes changed 

 to the form of fine threads or fibrils which are drawn out from the reticulum by 

 the receding membrane. The state of tension set up in the cytoplasm thus finds 

 an expression in the drawn-out threads of ' kinoplasm.' 



From the different plants studied it seems that the lines of tension as expressed 

 in the fibrils may group themselves in various ways at first. Thus we may 

 have a weft of kinoplasm about the nucleus ; or a system of kinoplasmic radia- 

 tions ; or more commonly a number of conical-shaped sheaves of fibrils. 

 But whichever form the kinoplasm may appear to take, the lines of tension 

 are constantly shifting throughout the prophase. Such a shifting does not 

 mean the changing of the threads bodily from one position to another. It 

 means the relaxing of the tension along certain threads — which would con- 

 sequently fall back into the reticulate form — and the setting up of new lines of 

 tension by the drawing out of threads from the undifferentiated reticulum. In 

 this fashion not only individual threads but entire sheaves or cones of fibrils may 

 appear to assume different positions. The generally accepted view that the 

 sheaves or cones approach one another and coalesce in two groups can be no 

 longer retained. There was no evidence to support the view that the spindle 

 fibrils grow into the nuclear area and attach themselves to the chromosomes. 

 This attachment is undoubtedly brought about by the enveloping of each bivalent 

 chromosome by the receding nuclear membrane. This investigation lends no 

 support to the view that the attached fibrils draw the daughter chromosomes to 

 the poles of the spindle. 



The achromatic figure as we see it in the vascular plants can no longer be 

 regarded as an active factor in mitosis. It is simply the passive effect or expres- 

 sion of a state of tension set up in the cytoplasm — a tension caused in the first 

 place by nuclear osmotic changes. 



8. The Longitudinal Fission of the Meiotic Chromosomes in Vicia Faba. 

 By Miss H. C. I. Fraser, D.Sc. 



In the telophase of the vegetative divisions the chromosomes of Vicia Faba 

 undergo longitudinal fission ; this fission persists, forming the line of separation 

 of the daughter chromosomes in the succeeding prophase. Fission takes place as 

 usual in the telophase of the last vegetative division in the archesporium, and 

 when the preparation for meiosis begins the reticulum consists of split threads 

 united to one another both by their ends and laterally. 



The longitudinal fission is recognisable throughout the synaptic stage, and is 

 responsible for the V shape of the chromosomes on the heterotype spindle. 



At the poles the V s come into contact, become attached to their neighbours, 

 and undergo a second longitudinal split. Both fissions are recognisable till the 

 chromosomes pass on to the homotype spindle, where, as a result of the first 

 fission, they still have the form of' Vs. The first fission—that initiated in the 

 last archesporial telophase — being now completed, the daughter chromosomes pass 

 up the spindle as rods. The second fission, obliterated during the metaphase, is 

 renewed as the chromosomes come into contact with their neighbours at the pole 

 and is recognisable in the haploid reticulum. 



