558 FILICALES 



cell is thus never actually immersed in the tissue of the receptacle as 

 is the case in Gl. flabellata. In this feature again, Gl. dichotoma approaches 

 the ordinary Leptosporangiate type. The central sporangia, above noted 

 as occurring in this species, arise, as far as can be seen, simultaneously 

 with the rest, and actually occupy the central area of the sorus from the 

 first (Figs. 311 h, /') ; this area is usually vacant in other species, and is 

 sometimes vacant also in Gl. dichotoma (Fig. 311 g). Since the sporangia 

 originate in this central position, their presence there cannot be accounted 

 for by displacement due to pressure ; it is to be ascribed rather to extra 

 development, or interpolation of one or more accessory sporangia, which 

 arise in a position usually unoccupied in the genus. 



The divisions in the sporangial head to form the lateral cells of the 

 wall, the cap-cell, the tapetum and definitive archesporial cell, follow with 

 slight deviations the type general for Leptosporangiate Ferns (Figs. 311 b-g) : 

 the archesporial cell is usually of tetrahedral form, but from the first it 

 is of relatively small size, while the tapetum, which soon divides periclinally 

 into two layers, grows rapidly. The outer wall remains a single layer of 

 cells, but the cells divide freely by anticlinal walls so that in the mature 

 state the sporangial wall consists of very numerous cells (Figs. 311 d, j, k). 

 The annulus soon becomes differentiated, and it appears that part of the 

 annulus owes its origin to the cap-cell, but the larger part to the lateral 

 segments. The outer layer of the tapetum with occasional supernumerary 

 cells near the attachment of the stalk remains small, and forms a narrow 

 inner investment of the wall ; it is permanent for a considerable time, 

 and traces of it may be found even in the mature sporangium. The inner 

 tapetal cells enlarge greatly, and often become polynucleate ; their pro- 

 toplasm becomes aggregated, with the nuclei in close proximity to the 

 sporogenous mass (Figs. 311 _/, /). while the cell-walls become 'absorbed. 



The definitive archesporial cell in G. flabellata undergoes successive 

 divisions (Figs. 311 d, _/), but the divisions are continued beyond the limited 

 number usual for Leptosporangiate Ferns ; the result is a very considerable 

 cell-mass, so that a single vertical section through a sporogenous group of 

 an average sporangium may traverse as many as 46 spore-mother-cells 

 (Fig. 311 _/) ; 45 was found to be the mean of countings in sections 

 through eight different sporangia. A section through a sporangium parallel 

 to the surface of the leaf may traverse even a larger number, as in the 

 sporangium of Fig. 311 /', where 66 are shown in section. This difference 

 may be in part due to the section traversing the curved sporogenous 

 mass obliquely, but this explanation will not account completely for the 

 variation in number. Any one section will only traverse about one-eighth 

 of the whole number of sporogenous cells, thus there will be about 

 45 x 8 = 360 spore-mother-cells in a single sporangium, and the potential 

 output of spores may be estimated at about 360x4=1440. Comparing 

 this with the case of ordinary Leptosporangiate Ferns, it is plain that the 

 potential productiveness of an average sporangium of Gl. flabellata is far 



