SPORE-PRODUCING MEMBERS 



455 



simpler, or reduction from a. more complex type, may be a question 

 for discussion ; but it is clear that the gradually transitional forms do 

 exist. 



As regards the first appearance of the sporangium, the essential parts 

 of it, though not the whole body, are normally referable to a single 

 parent-cell, and the first periclinal division delimits the sporogenous 

 tissue (see Figs. 43, 44, p. 88). It appears that here all the sporogenous 

 cells undergo the tetrad-division, and the nourishing tapetum, which is 

 entirely derived from the surrounding tissue, makes 

 its way inwards between the fertile cells. 1 As 

 regards vascular supply, a strand extends to within 

 two cells of the base of the cavity, and there 

 terminates. Finally, the dehiscence is as in 

 Ophioglossum. It thus appears that the whole 

 sporangium of Botrychium is of the Ophioglossum 

 type, but it is more definite and specialised in its 

 characters, and this goes naturally along with its 

 smaller size, which is most marked in B. virginiannm. 



It has already been noted that the position 

 of the fertile spike in Helininthostachys is similar 

 to that of Ophioglossum : it may further be added 

 that the origin of it is similar, and its structure 

 in early stages not unlike. It appears first as an 

 outgrowth on the adaxial side of the sterile frond, 

 and it is curved over while young, so that the 

 actual apex is pointed downwards : the whole of 

 the spike is at first covered and protected by 

 the segments of the sterile frond, which again are 

 protected by the stipular sheath. Since then, as 

 regards position, and the main facts of origin, 

 the whole spike of Helminthostachys may be 

 regarded as homologous with the whole spike of 

 Ophioglossum^ a special interest will attach to the 



origin and development of those bodies which directly bear the sporangia 

 in this genus, viz. the sporangiophores. 



Transverse sections of the fertile spike show at the lateral regions 

 corresponding to the sporangiogenic bands in Ophioglossum^ a fan-like 

 tracery of the cell-walls, while the surface is covered by a rather regular 

 series of deep cells : it is from these that the sporangiophores originate, 

 as outgrowths of very irregular size and arrangement (Fig. 254 A). Growing 

 first deeper, these cells divide by periclinal and anticlinal walls ; the 

 growth, however, is not uniform, but is localised at points so that 

 rounded processes, often of very unequal size, make their appearance 



1 Holtzman, Bot. Gaz., xvii., p. 214; Cardiff, Bot. Gaz., xxxix., p. 340; also 

 Studies, \\, p. 197. 



. 



FIG. 254. 



Helminthostachys zeylanica. 

 Young spike in oblique profile : 

 the primordia of sporangio- 

 phores are densely clustered on 

 the margin. Magnified. (After 

 Goebel.) 



