XIV 



ISOETACEsE 



553 



leaves continues up to about the eighth, when the i divergence 



is replaced successively by 



-|, -f, f 



and -fa, which is the con- 



dition in the fully-developed sporophyte. 



THE ADULT SPOROPHYTE (Sadebeck (p)) 



The structure of the mature sporophyte has been the sub- 

 ject of repeated investigations, among the most recent being 



FIG. 320. A, B, Isoetes echinospora. A, Section of fully developed leaf, Xis; B, 

 vascular bundle of the leaf, X about 200; C, part of a transverse section of the 

 stem of I, lacustris; sp, starch-bearing cortical cells; vn, meristematic zone; h, 

 tracheids; ltd, tissue of the central region (C after Potonie). 



those of Farmer (2) and Scott (2), who made a most careful 

 examination of the vegetative organs in /. lacustris and /. hys- 

 trlr. The thick, very short stem has a central vascular bundle, 

 which as in the young plant is made up of the united leaf-traces, 

 and there is no strictly cauline portion, as Hegelmaier ( I ) and 



