XIII 



LYCOFODINEAi 



515 



The protoplasmic layer is somewhat thicker at the apex, and 

 here begins the first cell-formation (Fig. 296, D, E). There 

 is but a single layer of nuclei at this point in S. Kraussiana. 

 In 6^ opus there may be, accr)r(ling to Miss Lyon, six or seven 

 layers; but none at all in the basal regicjn oi the spore. 



Cell-division begins in .V. Kraussiana by the simultanecAis 

 appearance of delicate cell-walls between the nuclei at the apex 

 of the spore. These walls cut out cells (areoles), each, at least 

 in the central region, containing but a single nucleus. These 



B. 



Fig. 297. — Sclaginella Kraussiana. A, Longitudinal section of a nearly ripe macro- 

 spore, with the primary prothalliuiji (Pr) complete, but still showing a large 

 vacuole in the centre of the spore, X65; B, similar section of a younger stage, 

 before the diaphragm has been differentiated, X400; n, free nuclei. 



areoles are at first open upon their inner side, and the first cell- 

 formation resembles to a remarkable degree the typical endo- 

 sperm formation in the Spermatophytes. Fig. 296, E shows a 

 cross-section of the apex of the spore shortly after the first cell 

 walls are complete. The extremely regular hexagonal form of 

 the cells toward the centre of the prothallium is very noticeable. 

 At the margin, and below, the cells are larger, and often contain 

 several nuclei. 



The cell-formation does not extend at this stage to the base 

 of the spore, as in Isoctcs, but is confined to the apex, where a 

 definite cellular body is formed. This is three-layered in the 

 middle, but at the margins but one cell in thickness. The lower 

 cells have the walls which are in contact with the spore-cavity 



