IX MARATTIACE^E—ISOETACE^ 291 



bundle formed from the coalescence of the bases of the bundles 

 from the leaves and roots. In all the later-formed leaves and 

 roots there is but a single axial bundle. In the leaves this is 

 decidedly collateral in form with the poorly -developed xylem 

 upon the inner (upper) side. Except for their larger size, and 

 their having usually four instead of two air-channels, the later 

 leaves resemble in all respects those first formed. 



The development of the young plant was not followed 

 beyond the appearance of the third leaf, but it probably in its 

 later history corresponds to /. lacustris. Here, according to 

 Hofmeister,^ the opposite arrangement of the leaves continues 

 up to about the eighth, when the |- divergence is replaced 

 successively by ^, |-, |-, y^'g, and -^^, which is the condition in 

 the fully-developed sporophyte. 



Tlie Sporophyte 



The structure of the mature sporophyte has been the 

 subject of repeated investigations, the most recent being those 

 of Farmer," who has made a most careful examination of the 

 vegetative organs. 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^ and Bruchman ^ assert. This central cylinder is 

 composed of very short tracheids, with spiral and reticulate 

 markings, mixed with similarly -shaped cells with thin walls. 

 Surrounding this xylem-cylinder is a layer of cells, which 

 Farmer calls the " prismatic layer." This, according to Rus- 

 sow,^ is continuous with the phloem of the leaf- traces, and 

 he regards it as the phloem of the stem bundle. Outside of 

 this prismatic layer is a zone of meristematic cells, which form 

 the " cambium." The cells of this zone are like those of the 

 cambium of Botrychiuvi or of the Spermaphytes, and like these 

 new cells are formed on both sides ; but those formed upon 

 the outside remain parenchymatous and are gradually thrown 

 off with the dead outer cortex, but those upon the inner 

 side develop into the prismatic cells, mingled with which are 

 cells very like the tracheids, except that they retain to some 



1 Hofmeister (l), p. 354. - Farmer (2). 



^ Hegelmaier (i). ^ Bruchman (i). 



'= Russow (i), p. 139. 



