152 MR A. ANSTRUTHER LAWSON ON 
diffusion, and the presence of the plasmatic nuclear membrane makes such a 
diffusion possible. As this gradual diffusion progresses and the volume of the nuclear 
vacuole decreases, the reticulate cytoplasm finds itself under tension in being obliged 
to occupy a greatly increased cubical space (compare fig. 31 with fig. 26). This 
tension finds an expression in a changed configuration of the reticulum. ‘This latter 
becomes drawn out in the form of threads by the diminishing and receding plasmatic 
membrane. 
A comparison of such stages represented in figs. 31 and 32 convinces me that the 
reduction of the karyolymph by diffusion does not cease when it becomes no longer 
visible as a clear nuclear sap, but continues until each chromosome becomes closely 
enveloped by the nuclear membrane. It will be seen from fig. 32 that each 
chromosome is not only thus furnished with a system of fibrils which become closely 
applied to its surface, but osmotic diffusion continues for some time, establishing new 
lines of tension. As in the case of Disporwm and Giladzolus, the main lines of kino- 
plasm extend from the broad sides of the chromosomes, and the tension thus becomes 
exerted on opposite sides, and at right angles to the long axis of each bivalent 
chromosome. These latter bodies thus find themselves suspended at the equator, as 
shown in fig. 33. 
HEDERA. 
With the object of extending the range of my observations into the Dicotyledons, 
I have selected the common ivy —Hedera helix—as a type for study. In the microspore 
mother-cells of this plant I find also a series of stages showing the persistence of the 
nuclear membrane throughout the prophase—stages which can only be interpreted in 
the manner for the monocotyledonous types, Disporum, Gladiolus, and Yucca. The 
nucleus, at the time the chromosomes are nearly formed from the spireme, occupies more 
than half the volume of the cell-cavity, as shown in fig. 34. In section the cytoplasm 
appears as a narrow zone filling the space between the nuclear membrane and the cell- 
wall. Its reticulate structure is uniform throughout. The chromosomes are small, oval- 
shaped bodies, and for the most part occupy a position in touch with the nuclear 
membrane. ‘The large nuclear vacuole is evidently under high osmotic pressure. It is 
almost spherical in form and in a state of turgescence. 
Fig. 35 represents a similar section at a somewhat later stage. It will be seen that 
the nuclear vacuole is much smaller than that shown in fig. 34. A certain amount of 
the karyolymph has evidently diffused into the cytoplasm, and this has been carried — 
still further in the stage shown in fig. 36. The conditions shown in figs. 35 and 36 are 
quite similar to corresponding stages in the mother-cells of Disporum. Accompanying 
the decrease in volume of the nuclear vacuole there is a change in the form of the 
cytoplasmic reticulum. It will be seen (fig. 35) that the reticulum, at one side of the 
nucleus, has been drawn out into a broad tuft of short threads or fibrils. It will also — 
be seen that as the nucleus becomes smaller and smaller (fig. 36), the kinoplasmie 
