340 Watson on Structure and Relation of the Plastid. 
Vaucheria, Oscillaria.—In the former the chlorophyll is 
distributed in plastids of varying size in the cell protoplasm. 
In Oscillaria the condition is still more primitive, and the 
chlorophyll green is diffused throughout the protoplasm with 
no attempt at localization. 
Coleochaete has a similar diffuse chlorophyll structure. The 
nuclei stain densely, of a density similar to that of pyrenoids, 
and in many instances show small refractive nucleoli. These 
nuclei are situated at or very near the center of the cell and 
are surrounded by a rather clear area. This area, however, 
is not bounded by a membrane of any kind. 
The nuclei of Coleochaete suggest in their appearance the 
pyrenoids of preceding plants, while their contained nucleoli 
resemble, in their strong refraction and density, the nucleus 
of Zygnema. 
Nitella——In this plant the plastids are arranged in long 
parallel rows close beneath the cell wall and are held together 
against the force of circulating protoplasm by branching 
strands, which place the whole system in communication. 
There seems to be no regularity of branching of these 
strands, the whole merely forming an irregular network. 
The strands take the eosin stain slightly, but owe their dis- 
tinctness to their refractive character, and also to the gran- 
ules adherent to their substance. 
The plastids are of a uniform, quite densely staining char- 
acter and divide by simple fission. Fig. X (d) shows a 
plastid dividing; while (s) represents two plastids just after 
completion of the septum. 
Anthoceras.—The plastids of this plant are joined together 
by interplastid fibres and form a general network system as 
in Nitella. The plastids are of a large, quite densely stain- 
ing character, and exhibit a finely granular structure. Along 
the interplastid fibres are distributed numbers of fine gran- 
ules seemingly of the same nature as those within the plastid 
(Fig. XIT). 
The nuclei are of large size and their substance of a 
