XIII] 



THE STALK OF THE SPORANGIUM 



247 



segmentation {Platyceriiwi). This indicates that the reference of such parts 

 to the initial segmentation in any special case studied has no fundamental 

 significance, for it is not generally applicable. It appears in this as in other 

 examples that there is no general or necessary relation between initial 

 segmentation and the production of mature structures. 



The Stalk of the Sporangium 



In the deeply immersed sporangium of Ophioglosstwi it is impossible to 



recognise any stalk at all. But in Botrychium, in which the sporangium 



projects, the stalk is a massive column. In B. dmicifolimn it is about six 



layers of cells in thickness (Fig. 242, c). A vascular strand may curve into each 



Fig. 242. a, l>, c, successive stages of the development of the sporangium in Botrychiuni daucifolium . 

 ( X 250.) Compare the massive stalk with those shown in transverse section in Fig. 243. 



sporangium, stopping short below the capsule itself. But it is only in the 

 largest sporangia of Ferns that there is any individual vascular supply : when 

 the stalk is less massive there is none, as mAngiopteris where the stalk consists 

 of about three layers of cells (Fig. 244). Passing from these Eusporangiate 

 Ferns to those Leptosporangiates styled the Simplices, the relatively large 

 sporangia have usually short stalks. In some of the largest of them the stalk 

 consists of a central column of cells surrounded by a superficial series, as in 

 Gleichenia circinata, and sometimes in Osninnda (Fig. 243, a, d). In others the 

 central column is represented only by a single cell-row {e, i, h), but in most 

 of the Leptosporangiates this is absent. The transverse section of the stalk 

 then shows a radial segmentation, as in Fig. 243, b, c,f, i, etc. and this leads 



