II MUSCINEJL— HEPATIC AL—MARCHANTIACE^ 35 



are periclinal, and by them a single layer of outer cells is 

 separated from the central mass of cells which constitutes the 

 archesporium (Fig. 6, B, D). 



At first the cells of the embryo are much alike, but as it 

 grows the inner cells increase in size and their contents become 

 densely granular, while the outer cells grow only in breadth, 

 and not at all in depth, assuming more and more a tabular 

 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 gobular cell with thin membrane 

 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. fn embedding these in parafifine, 

 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. 



Fig. 7, A shows the nucleus of the mother cell under- 

 going the first division. The small size of the nuclei, and 

 the small amount of chromation in them, make the study 

 of the details of the nuclear division difficult here, and as 

 there was nothing to indicate any special peculiarities these 

 were not followed out. After the first nuclear division the 

 daughter nuclei divide again, after which the four nuclei 

 arrange themselves at equal distances from each other, the 

 division walls form simultaneously between them, dividing 

 the spore mother cell into the four tetrahedral spores. A 

 section through such a young spore-tetrad is shown in Fig. 

 7, B, where one of the cells is somewhat shrunken in the 

 process of embedding. The cell walls at this stage are very 

 delicate and of unchanged cellulose ; but as they grow older 



