208 PROCEEDINGS OP THE AMERICAN ACADEMY 



relations to each other as the internal and external central cells, and 

 a'^ain the place occupied by the internal and external central cells 

 may be filled by a single cell. This latter case is comparatively rare, 

 and where it has been observed the single cell was always next the 

 marmnal series. 



By carefully treating the spore-mass with a hot solution of potassic 

 hydrate, maceration was effected, and a pair of cells thus obtained is 

 shown in Figure 7. The larger of these two is an external, the smaller 

 an internal central cell ; it is, however, as frequent an occurrence to 

 find two internal or two external cells attached, as to find a group 

 similar to that figured. The adhesion seems to be equally strong 

 between all contiguous cells, and the grouping of incompletely macer- 

 ated material is in consequence largely accidental. 



The cells obtained by maceration lose their slightly angular outline, 

 and become somewhat swollen. From the sections (Figs. G and 8), 

 and from the isolated cells (Fig. 7), it will be seen that the outer walls 

 of the external central cells, as well as the same walls of the marginal 

 cells, are very much thickened, while those walls which are not ex- 

 posed to the surface, but face contiguous cells, are thin. All the walls 

 of the internal central cells are thin except those which are next the 

 cyst region ; these latter are of moilerate thickness. 



The line of separation between adjoining cells is usually discovera- 

 ble without resort to reagents (Fig. 4) ; nevertheless difficulty may be 

 experienced in separating two of the thin walls of adjacent cells. This 

 difficulty can be overcome by checking the maceration process just 

 before completion, when the lines of reparation will have become well 

 marked (Fig. 7). All the spore-cells contain a coarsely granular 

 protoplasm, in the centre of which a nucleus may usually be discerned 



(Fig. 7). . 



The cyst region is composed of a number of rounded, transparent, 

 thin-walled cells, forming a cluster somewhat smaller than the spore- 

 mass itself, and connecting the latter with the stem region (Fig. 10). 

 From the exterior it is diificult to make out the relationship existing 

 between the cyst-cells and those of the spore-mass. In longitudinal 

 sections, however, it may be seen (Fig. 8) that below each margi- 

 nal cell and each pair of central cells there is a cyst-cell. This rela- 

 tionship seems to be almost invariable, — at least, in a long series of 

 observations no exception has as yet occurred. 



The individual cells in the centre of the cluster, from mutual pres- 

 sure, are more or le?s angular. Those on the periphery have at least 

 their outermost side convex, and often very dciidedly so (Fig. 10). 



