588 Murrill .— The Development of the Archegoninm 
the sheath-nuclei, but the sheath-cells are never found without 
their nuclei. The sheath remains one-layered, though its 
cells often divide as the archegonium grows. At points 
where the archegonia come into close contact (Fig. 16), the 
sheath is frequently crushed and destroyed, but throughout 
most of its extent the cells and their nuclei continue active 
during the life of the archegonium. 
The Formation of the Ventral Canal-Cell. 
Shortly before the division of the central cell, an accumu¬ 
lation of cytoplasm may be observed beneath the nucleus a 
little to one side of the longitudinal axis of the archegonium 
(Fig. 13). This accumulation is a dense mass of fibres with 
small granules of uniform size scattered through it, the whole 
being continuous with the cytoplasm around it and taking 
the same brownish stain with the Flemming combination. 
From the first it is closely pressed against the nuclear mem¬ 
brane, and soon begins to push it inward in the form of blunt, 
unequal projections (Fig. 17). This fibrous mass continues to 
increase in size and to send out radiations far into the cyto¬ 
plasm, thus forming a support for the free lower pole. These 
radiations grow at their free ends from the cyto-reticulum 
and extend in all directions, but are of necessity short on the 
side next the nucleus. 
The spindle-fibres arise within this mass and grow upward 
against and press in the nuclear membrane, while they also 
draw to a point below and establish the lower pole of the 
spindle (Figs. 18-21). At the pole there is usually greater 
density and frequently a rounded granule (Fig. 24), but 
nothing could be discovered corresponding to a centrosome, 
even with the most favourable methods. Activity at the 
upper pole begins late and is always feeble. The cytoplasm 
between the nucleus and the neck-cell is all of a density 
intermediate between that of the ordinary cytoplasm and that 
collected at the lower pole. In a few cases a minute hyaline 
lenticular area was observed at the upper pole, resembling 
the collections of sap usually seen between the polar caps of 
