Beer . — On the Development of the Spores of Riccia glctzica. 277 
the condition is entirely due to them. During the isolation of the spore- 
mother-cells from one another the sporangial cavity enlarged considerably. 
Taking the measurements from the periphery of the outer of the two layers 
of the archegonial wall the diameter of the cavity at such a stage as that 
shown in Fig. 29 is about 240 jm, whilst when the mother-cells are rounding 
off (as in Fig. 30) it has increased to about 300 or 345 jut. 
Garber and Lewis have both described a large amount of nutritive 
material which fills the space between the mother-cells and which is secreted 
by the surrounding cells. In my preparation of Riccia glauca I have seen 
nothing of this material 1 . 
The rounded mother-cells now proceed to divide. The following 
description is based upon the study of preparations which have been stained 
with Heidenhain’s haematoxylin, either alone or with a light counter stain 
with bismarck brown. The large nucleus of the spore-mother-cell just 
before the commencement of division contains a conspicuous, deep-staining 
nucleolus and a number of delicate linin fibres which have little affinity for 
dyes (Figs. 1 and 2). In these features the resting nucleus of the sporo- 
genous cells of Riccia glauca differs from the description given by Lewis 
for the two species which he has studied. He found the nuclear cavity to 
be occupied by a linin network upon which the scanty chromatin is 
irregularly scattered ; moreover he states that no nucleolus was to be seen. 
I have examined a large series of sections of sporangia containing mother- 
cells at all stages up to their maiotic division, but I have never observed a 
nucleus which contained a reticulum such as Lewis figures, nor one which 
was without a nucleolus. In the case of Riccia glauca , therefore, we can be 
certain that no such non-nucleolated, reticular resting stage occurs. 
It may also be added that the resting condition of the vegetative nuclei 
of the thallus of Riccia glauca agrees essentially with what I have described 
above in the case of the sporogenous cells. 
The nucleolus in nearly all cases has a lobular outline (Fig. 1) and I 
believe that this is due to the fact that the nucleolus is not a homogeneous 
body, but is composed of a number of small chromatic masses or granules held 
together by a common matrix. These granules are usually so closely crowded 
together in the nuclei of the sporogenous cells that it is not easy to see their 
separate individuality. In a few cases, however, the nucleolus was actually 
seen to be composed of distinct granule-like bodies which had become 
rather more widely separated from one another than usual by the action of 
the reagents employed or through the pressure of the microtome knife 
(Fig. 2) 2 . In the vegetative nuclei at the growing apex of the thallus the 
constitution of the nucleolus can be much more readily determined when 
1 See Garber, 1 . c., Plate X, Fig. 37. 
2 Compare also Fig. 16, in which the separate chromatin granules of the earlier stages of 
division are massing together to form one body. 
