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. rulgatum 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. 1 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 

 as well as that of 



FIG. 250. 



Opltioglossuui reticulatniii, L. Longitudinal section 

 through a sporangium before separation of the spore- 

 mother-cells ; the walls of the vascular tissue are drawn 

 the fertile Spike Which it bears, in rather more heavily. X ioo. 



has been described by Bruchmann 



for B. Lunaria.* He found that the fertile spike originates in the same 

 position relative to the sterile leaf as in Ophioglossnm, 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 



1 The statement of Rostowzew that ;i 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. vulgatitni were lent by Professor Fanner, has shown that this is an error ; as had 

 been already noted for O. reticitlalnin by Burlinghame (Bot. (Ja~., July, 1907, p. 34). 

 Occasional cells may be disorganised (Fig. 251 u), as may happen in any large sporangia; 

 but normally there appears to be no systematic disorganisation, such as is seen in 

 E</itis,-tiii or the Psilotaceae. 



-Flora, 1906, p. 213. 



