XIX] 



DEVELOPMENT OF SPORANGIA 



71 



from one of the latest adaxial segments of the leaf-initial {I.e. Fig 363). Both 

 parts retain their active initial cells till about the time of origin of the lateral 

 pinnae. He describes how the origin of these in Botrychiuni is by a process 

 quite distinct from that of the fertile spike: the latter appears in a median 

 position with a definite apical cell from the first: the pinnae arise in acropetal 

 order by marginal growth {I.e. p. 2 1 8). Steps in development of the sporangia 

 of BotryeJiiiuii, normally separate from one another, are shown in Fig. 370. 

 The sporangium is eusporangiate, but the sporogenous tissue originates from 

 a parent cell that is the inner product of a single superficial cell which 

 divides periclinally. The stalk is thick : the wall may consist of several layers 

 of cells, and the spore-output of the sporangium is large. A peculiarity is that 



Fig- .^70. a, b, (-, successive stages of the development of the sporangium in 

 Boti-yihiitm daiuifoliitm. ( x 250.) Note the very massive stalk, 



each sporangium may have its own vascular supply by a strand which 

 terminates immediately below the capsule. This is an exceptional condition 

 in living Ferns, but it has its parallel in the fossil Stauropteris. A further 

 point is that the identity of the sporangia is not always maintained. In 

 B. Limaria sporangia may be found coherent together, and this condition 

 has been worked out developmentally in the larger B. daueifolium, in which 

 such cohesions are more frequent (Fig. 371). The drawings A — C7 show 

 sporangia of the normal type; but others (Z>, E) have a broader form, 

 leading to a doubling of the sporogenous group: it is only a slight step from 

 E to F or G, that is, to a state where two distinct sporogenous groups are 

 present, with a rounded contour for each. Such examples illustrate gradual 



