186 Drew .— The Reproduction and early Development of 
cells in each row depends on its position, the rows at the apex and base 
containing fewest cells. In later stages, as the apex becomes relatively 
more pointed, this definite arrangement is lost. Each cell shows a central 
area coloured brown by the presence of the chromoplasts, and a clear 
peripheral region. The central portion stains an intense mahogany brown 
with iodine. 
This division of the protoplasm into two regions is found under natural 
conditions and does not appear to be due to any plasmolytic action. 
The cell-walls are extremely delicate and somewhat difficult to resolve 
unless oblique illumination be used. 
There is a single nucleus in each of these cells, situated near the centre : 
this can be demonstrated by staining with dilute nuclear stains after fixing, 
and decolorizing the chromoplasts with alcohol. 
Development of the Young Plant. 
The lamina now increases in size owing to active cell-division. The 
cells near the base divide into two, in a direction at right angles to the 
plane of the lamina, which thus becomes two cells thick. These then again 
divide, and the outer cells go to form the limiting layer, whilst the inner 
form the cortical layer. The apex and periphery of the lamina remain one 
cell thick. The narrow basal portion of the lamina, to which the rhizoids are 
attached, increases in thickness and forms an oval stalk which constitutes 
the rudimentary stipe (Figs. 8 and 9). In this, the layers of cells of the 
cortical tissue are thicker than in the lamina. There will obviously be 
two layers of cortical cells which meet in the centre; each layer is derived 
from one of the two cells formed by the first division of the primary cells of 
the lamina. Usually in sections a small space is noticeable between these 
two layers, but this may be due to distortion produced by treatment with 
alcohol when cutting serial sections. Owing to the minute size of the 
plants it was found impossible to cut sections by the freezing method 
in this stage of growth. 
The next stage appears to consist in an upgrowth of tissue from an 
active growing point, originating in the cells to which the rhizoids are 
attached. In this way chains of elongated cells are formed which grow up 
between the two layers of the cortical tissue. At the same time the inner¬ 
most cortical cells divide, and certain of them start active growth, forming 
chains of much elongated cells, somewhat resembling fungal hyphae in 
appearance. These cells ramify among those growing vertically upwards 
from the base, and the whole mass thus formed is embedded in a structure¬ 
less hyaline matrix. This material seems to be secreted by the cells them¬ 
selves ; it stains strongly with safranin, and also with haematoxylin, and is 
probably of a mucilaginous nature (PI. XV, Figs. 13 and 14). 
