3 
Davis. — Spore Formation in Derbesia . 
gradual formation of a thick ring at the base of the sporangium. Sec- 
tions of this ring (Fig. 4) show that its substance (evidently cellulose in 
character) is laid down in concentric layers on the inside of the wall 
of the filament at the base of the sporangium. The protoplasm of the 
sporangium is thus gradually pinched off from that of the filament and 
is not separated by thin cleavage furrows as in the sporangia of the moulds. 
The ring-like deposit thickens and finally becomes a heavy plate 
of cellulose (Fig. 5), which presents a laminate structure, showing that 
its substance is deposited in successive layers as the protoplasm in the 
sporangium and in the filament withdraw from one another. The wall 
shown in Fig. 5 is from a sporangium in which the protoplasmic 
cleavage to form the spores had already begun. 
The Differentiation of the Nuclei in the Sporangium and 
the Degeneration of the smaller Nuclei. 
The nuclei which enter the developing sporangium are similar and all 
of about the same size and a little larger than the plastids (Fig. ’6). Each 
contains a small deeply-staining nucleolus which frequently lies within 
a clearer circle. The remainder of the nuclear cavity is almost wholly 
occupied by a large body which stains lightly but is readily distinguish- 
able. This body is probably chromatic in character as shown by its 
later history, but at this stage it is homogeneous and gives no indica- 
tion of granular or fibrillar structure. There must be several thousand of 
these nuclei which enter the developing sporangium. 
The nuclei begin to show a differentiation in size very shortly after 
the protoplasm of the sporangium becomes separated from that of its 
parent filament or even before this time. Certain of them increase in 
size and become conspicuous in the sporangium, finally reaching a diameter 
4-6 times the size of the plastids (Fig. 8). The large nuclei may have 
smaller nuclei very near them, singly or in groups, to which they appear 
in sharp contrast (Fig. 7). The internal structure of the nucleus does not 
apparently change during its growth. The large homogeneous chromatin 
body, however, increases in size. 
There are, however, marked changes in the appearance of the proto- 
plasm around the enlarging nuclei. A granular cytoplasm forms an 
envelope so that the plastids come to lie at some distance from the nuclear 
membrane (Fig. 9), and delicate protoplasmic strands radiate out from the 
membrane between the plastids into the surrounding protoplasm (Fig. 9). 
These strands end in deeply-staining granules just outside of the nuclear 
membrane. The large nuclei are thus very prominent in the sporangia 
because of their size and the radiating strands from the enveloping zone of 
granular protoplasm bordered by the plastids. 
