34 



MOSSES AND FERNS 



CHAP. 



form, and for the most part undergo divisions only in a radial 

 direction so that the walls remain but one cell thick in most 

 places. As the sporogonium increases in diameter the central 

 cells begin to separate and round off. Their walls become 

 partially mucilaginous, and in microtome sections stain 

 strongly with Bismarck-brown or other reagents that stain 

 mucilaginous membranes. With this disintegration of the 

 division walls the cells separate more and more until they lie 

 free within the cavity of the sporogonium. Each of these 

 spore mother cells is a large globular cell with thin membrane 



m. 



Fig. 6. — A, B, Young embryos of R. glauca in longitudinal section, showing the 

 venter of the arehegonium, X260; C, transverse section of a similar embryo, 

 X260; D, longitudinal section of the arehegonium and enclosed embryo of R. 

 trichocarpa at a later stage, X220; m, the sterile cells of the sporogonium. 



and densely granular contents. The nucleus is not so large as 

 is usually the case in cells of similar character, and, except the 

 nucleolus, stains but slightly with the ordinary nuclear stains. 

 In the fresh state these spore mother cells are absolutely opaque, 

 owing to the great amount of granular matter, largely drops of 

 oil, that they contain. In embedding these in paraffine, 

 however, the oil is dissolved and removed, and microtome 

 sections show the fine granules of the cytoplasm arranged in a 

 net-like pattern, the spaces between probably being occupied 

 by oil in the living cells. 



