Osborne^ on the Wheat Plant. 
115 
matter has also given to me evidence of another process of cell- 
growth. I have stated that where the formative matter becomes 
closely aggregated^ either in nuclei or in the masses with a less 
defined form^ it takes from the pigment a darker hue. This 
has shown me that the cells in some root structure are pro- 
duced on what appears to be a very simple plan. A large 
amount of the formative matter will have taken up the 
colour u.sed; on its surface you trace a network of plasm 
floated out ; the lines of this will be seen to dip down into 
the masSj and to form septa of some breadth^ thus dividing 
the granular coloured matter into quadrangular cells : by 
close observation with a high power it will be seen that these 
septa are not composed simply of the deposit of one layer of 
plasm^ but of several (PI. IV^ fig. 27). The matter thus 
divided and coloured will occasionally (it may be from the 
action of the preservative fluid I use) shrink up into folds 
within each division; it is then made evident that besides 
the cell-walls the granular contents of a cell are enveloped 
or blended in their own particular tissue. 
After giving much attention to the subject^ using the 
highest powers of the instrument_, and many difl*erent kinds 
of illumination^ I have arrived at the conviction that nuclei, 
when seen in cells, either alone or with vesicular investment, 
are exterior to — have a separate existence from the other 
granular contents of the cell. Now, I am quite satisfied that 
the plasm which forms the cell-walls consists of several 
layers; if, as I conjecture, these layers are continuous, i. e., 
extending without interruption from one cell to the next, I 
can easily conceive the facility with which a cell formed 
external to the surface of the enclosed granular matter could 
extend itself between any of these layers, and thus force its 
way into a distinct existence, increasing the bulk of the 
structure of which it formed a part. I am confirmed in this 
view from observing the extremely elastic nature of the cell- 
wall plasm. The apex, even of the youngest root, requires 
considerable pressure before it can be so broken up as to 
admit of being made into a preparation capable of being 
studied with a high object-glass. 
A transverse section of a root will sometimes show the 
dark masses of young cells, when in vigorous growth, forcing 
their way through the angular spaces formed at the points of 
contact of the divided cells; frequently they will be seen 
pushing their way on one side of the interior of those cells. 
I hold, then, these nuclei to be a very close aggregation of 
formative matter, by some law combined in the globular form, 
and sustained in that form by means of the viscous material 
VOL. V. ' k 
