SPORE-PRODUCING MEMBERS 451 
to it, as in certain other Pteridophytes, by successive periclinal divisions. 
The structure of the sporangium as it approaches the stage of separa- 
tion of the spore-mother-cells and of the tetrad-division is shown in 
Figs. 249 and 250: in the latter the relation of the vascular strands to 
the sporangium is already clearly indicated, especially of those which pass 
outwards in the thickness of the septum. The tapetum appears to be 
variable ; in O. vulgatum it consists of several ill-defined layers of cells. 
This is seen in Fig. 251 a, B, which illustrates the steps leading to tetrad- 
division in that species: the cells of the tapetum first lose their identity, 
their protoplasts fusing into a continuous plasmodium surrounding the 
sporogenous cells, while the nuclei 
persist, and apparently increase in 
number by fragmentation. The 
plasmodium penetrates between 
the sporogenous cells, the whole 
mass being first broken up into 
irregular blocks (Fig. 251 a), and 
later into individual cells (Fig. 
251 B). Normally all these spore- 
mother-cells undergo  tetrad-divi- 
sion, and form spores! When 
ripe each sporangium bursts by 
a horizontal slit, already defined 
structurally in the tissue of the 
wall: it gapes as the tissues dry 
up, but there is no mechanical 
annulus. 
The origin of the leaf in 
: 8 Ophioglossum: reticulatum, L. Longitudinal section 
Botrychium, as well as that of through a sporangium before separation of the spore- 
the fertile spike which it bears, She ek et eee 
has been described by Bruchmann 
for B. Lunaria.2 He found that the fertile spike originates in the same 
position relative to the sterile leaf as in Ofphioglossum, but much 
nearer to its apex; indeed, at the period when they may first be 
recognised by their respective initial cells, these are in close proximity to 
Fic. 250. 
1The statement of Rostowzew that «a large number of spore-mother-cells are dis- 
organised, and contribute with the tapetum to the nutritive plasmodium, was adopted 
by me in Studies, ii., p. 20, as it appeared to accord with my own rather limited 
observations. A re-examination of the question, for which a number of slides of 
O. wulgatum were lent by Professor Farmer, has shown that this is an error; as had 
been already noted for O. reticulatum by Burlinghame (Bot. Gaz., July, 1907, p. 34). 
Occasional cells may be disorganised (Fig. 251 B), as may happen in any large sporangia ; 
but normally there appears to be no systematic disorganisation, such as is seen in 
Lquisetum or the Psilotaceae. 
2 Flora, 1906, p. 213. 
