620 DR A. ANSTRUTHER LAWSON ON 
methods is the conversion of the living substance into a non-living artificial precipitate 
without essentially modifying its general form and configuration. The knowledge we 
now have of the minute structure of the cell and its organs has been based almost 
entirely upon the interpretation of such precipitates. 
I have had this in mind throughout the present investigation, and I have en- 
deavoured whenever possible to express my interpretations in terms of the lving cell. 
Helpful as this has been in elucidating many obscure points, I nevertheless fully 
realise that any theories or hypotheses, based upon a study of such precipitates, 
must at most be tentative. They should be freely subjected to modification or even 
abandonment whenever more certain and exact information becomes available. 
It seems very evident, from this investigation, that there are two physiological 
features which stand out above all others, as fundamentally important in the merismatic 
activities concerned. One of these is osmosis, and the other is the high state of nutrition 
that prevails. 
These. two features are, to a certain degree, related to one another, but the effects 
they produce are quite distinct. For instance, nuclear osmotic changes are responsible 
for the formation of the achromatic figure, while the high state of nutrition that pre- 
vails is concerned in the acceleration of the mitotic changes. 
All that series of changes in the cytoplasm which characterise the prophase, can, in 
my opinion, be interpreted in no other way than that of nuclear osmotic transfer. The 
oreat changes that occur in the relative positions of the nuclear and cytoplasmic sub- 
stances seem reasonably explained on this basis. As a result of these changes, the cyto- 
plasm is obliged to occupy a greatly increased space, and it is my opinion that this cannot 
be accomplished without a stretching or a tension being set up in the viscous structure of 
its reticulum. To me the evidence seems quite convincing that this tension or stretch- 
ing finds an expression in the changed configuration of the cytoplasm to drawn-out 
threads or fibrils. The evidence was also overwhelming in support of the view expressed 
that the fibrils of the mature achromatic figure are such drawn-out threads of cytoplasm 
and merely represent lines of tension. The conclusion naturally follows that the 
achromatic figure plays no essential or active réle in mitosis. It is simply an ex- 
pression of a state of tension that is produced as a result of changes in the nuclear 
osmotic relations. 
The high state of nutrition that prevails in the cells during meioses is a physiological 
condition which must be considered of prime importance in this connection. The 
effects it produces are quite different from those caused by nuclear osmotic changes, but 
nevertheless characterise the whole meiotic period. In somatic meristems a high state 
of nutrition no doubt exists, but in the meiotic meristem (spore mother-cells) the 
state of nutrition is very much higher. This difference—although it may be only one 
of degree and not of kind—is in my opinion sufficiently great to find an expression in 
the marked differences between somatic and meiotic nuclear phenomena. For instance, 
as everyone knows, the merismatic activity of meiosis shows itself by two divisions 
