TRANSACTIONS OF SECTION K, 567 
There are very few cells which do not show a trace of this foam structure at 
some stage or other in their development. It is very commonly seen in plant 
cells, and is especially pronounced in cells in which there is any kind of metabolic 
activity, and is very often displayed in cells in which disintegration is taking 
place. The cells of the larger Cyanophyces frequently show this when they are 
in the preliminary stages of disintegration. In the actively growing cells of yeast, 
in the odspheres of fungi, and in sexual cells of the higher plants, it is commonly 
well displayed. On the other hand we may often find in vegetative cells, in which 
there is very little metabolic activity, a complete absence of foam structure. 
In such cells we can, however, easily cause it to appear by subjecting them to 
pressure or heat, or to the action of reagents. In cells of living Euglens, for 
example, which are subjected to gentle pressure under a cover-glass, the clear 
homogeneous regions of the cytoplasm soon become filled with a beautiful vacuolar 
structure. In some vegetative cells we find that parts of the cytoplasm exhibit a 
foam structure, whilst others do not; this is no doubt to be associated with local 
activities in the cell. Such cases can be very easily seen in the cells of the 
staminal hairs of Tradescantia and the epidermal cells of the leaf. 
Strasburger considers that the cytoplasm is of two kinds, which he calls 
kinoplasm and trophoplasm. The kinoplasm exhibits a fibrillar structure, the 
trophoplasm an alveolate structure. The kinoplasm is that part of the cytoplasm 
which is active in the mechanics of cell-division and forms the fibres of the spindle, 
astral radiations, and such structures as centrosomes and blepharoplasts. The 
trophoplasm is to be regarded as nutritive in function. The great objection to 
this hypothesis is that it is only at certain periods in the cycle of changes which 
the cell undergoes that these structures are visible; at other times the kinoplasm 
cannot be distinguished from other parts of the cytoplasm, and it cannot be satis- 
factorily demonstrated that any one part of the cytoplasm is likely to be more 
active in the mechanics of division than another. 
From this brief discussion of the question itis, I think, obvious that we cannot 
come to any very definite conclusion as to whether a foam structure is an essential 
attribute of cytoplasm or not. But from the fact that cytoplasm appears homogeneous 
under certain conditions, and that the foam structure can be so readily produced in 
it by various means, and further that, as Hardy has shown, the action of certain 
reagents upon colloids results in the separation of solid particles which become 
linked together to form a comparatively coarse, solid framework in the form of an 
open net which holds fluid in its meshes, it is probable that we shall find the foam- 
structure theory of protoplasm is not tenable. It seems far more in accordance 
with what we know that we should regard protoplasm as fundamentally a semi- 
fluid, homogeneous mass, in which, by its own activity, granules, vacuoles, 
fibrils, &c., can be produced as secondary structures; and that any special 
morphological structure which it may possess is beyond the limits of the present 
resolving powers of the microscope. 
The Structure of the Nucleus. 
From the recent observations of Gregoire and Wygaerts, Berghs, Allen, 
Mano, and others, it is difficult to arrive at any definite conclusions as to the 
structure of the nucleus, or as to the changes which take place in it leading to the 
production of the chromosomes. The resting nucleus seems to possess a very 
simple organisation. In the living condition it appears to consist merely of a 
homogeneous ground substance in which is contained a mass of chromatin granules 
which do not appear to have any particular shape, and one larger granule of a 
spherical shape, the nucleolus. Sometimes a network or foam structure is visible, 
but not always; but here, as in the cytoplasm, it is difficult to be certain of this. 
It may be that the chromatin is always in the form of an irregular network 
embedded in the colourless ground substance, and that the granular appearance 
is due to an optical effect similar to that observed in finely meshed oil-foams. 
According to Strasburger, Miss Sargant, Farmer and Moore, Mottier, and others, 
the nucleus contains an achromatic network—the linin——in which the chromati: 
