454 



OPHIOGLOSSALES 



corresponding in every other respect, do not assume the dense 

 protoplasm of sporogenous cells. These more bulky sporangia lead 

 on to such as that shown in Fig. 253 E, in which it is possible 

 that the whole sporogenous group is referable to a single parent cell, 

 though the proportions of the whole group are quite different from those 

 of the typical sporangia ; the sporogenous cells appear, however, to form 

 two groups, and probably originated from two similar cells side by side. 

 The interest of this lies in the fact that these broad sporangia approach 



FIG. 253. 



Botrychium daucifolium, Wall. A and C, successive stages of the most common type 

 of sporangium. B = a small sporangium of narrow form. D = a very broad sporangium; the 

 cells marked (x) correspond to the sporogenous group, but showed no signs of developing 

 further as such. =a still broader sporangium with wide sporogenous group, referable 

 to two parent cells, possibly ultimately to one. F, G = synangia cut transversely and 

 vertically. X 200. 



in their form and bulk to the synangia which, as above noted for 

 Botrychium Lunaria, are not unfrequently found ; one of these, cut 

 through transversely, is shown in Fig. 253 F ; here there is a zone of three 

 layers of sterile tissue forming a septum between the two sporogenous 

 groups. The septum is, however, commonly broader than this : if a 

 comparison be made between this and the young synangia of Tmesipteris 

 the similarity will be readily seen. Such examples as these, which can 

 easily be found in sections of the fertile spike, illustrate the gradual 

 transitional forms which may be traced between the simpler and more 

 complex spikes of the genus. Whether these steps will bear an evolu- 

 tionary interpretation, as illustrating the manner of advance from 



; 



