424 Campbell. — Studies on the 
to be composed of crowded granules, and it seems probable 
that the apparent nucleolus is really composed of chromatin ; 
the structure being, perhaps, comparable to that of the nucleus 
of Spirogyra and some other Algae. 
The protoplasmic layer thickens more rapidly at the apical 
region, where the nuclei are also more numerous (Figs. 6, 8). 
Instead of the nuclei at the apex being in six or seven layers 
as described by Miss Lyon for the species examined by her \ 
in .S'. Kraussiana they are mainly restricted to a single layer, 
although there may be an occasional nucleus below this 
(Fig. 8). In regard to the first cell-formation, Kraussiana 
seems to differ widely from either 5. apus or 5. rupestris. 
There is no trace of the preliminary blocking out of proto- 
plasmic areas by protoplasmic fibrillae, but the first divisions 
are effected at once by cell-walls (Figs. 8, 9). These form 
simultaneously between the nuclei in the central part of the 
apical region, precisely as in ordinary endosperm-formation. 
The central cells (areoles) thus formed are regularly hexa- 
gonal in form, and usually contain but a single nucleus. 
Toward the margin of the prothallial disc they are larger and 
more irregular, and may contain two or more nuclei. Whether 
the formation of these walls is immediately preceded by 
nuclear division could not be determined. Faint indications 
of connecting fibres between the nuclei could be seen in some 
cases, but these were not very evident, and in the few cases 
where the young walls were found all of the nuclei were in 
the resting stage. 
The areoles thus formed are open below (Fig. 8), but between 
this stage and that where the prothallial disc was complete no 
stages could be found, and the exact method by which the 
subsequent cell-formation takes place must be left for future 
investigation. Presumably the next nuclear divisions are in 
a radial direction, and are accompanied by the formation of 
cells-walls which result in the development of the definite 
cellular disc, or primary prothallium which is found at the 
apex of the ripe spore (Fig. 10). This disc consists of 
1 1. c. p. 182. 
