124 Bristol . — Life-history and Cytology of Chlorochytrmm grande. 
No differentiation of a chloroplast is indicated in these stained sections, 
and it seems highly probable, both from this and from the external appear- 
ance of the cell, that the chlorophyll is diffuse throughout the cytoplasm. 
The cells of the colourless branching tubes which form the vegetative 
thallus appear to be quite empty, no trace being evident in the stained 
preparations of either cytoplasm or nuclei. 
Summary. 
In rain-water rapid multiplication of Chlorochytrinm grande takes place 
by means of aplanospores, and the cells are thin-walled. In mineral salt- 
solutions aplanospores are formed more rarely, and the cells become con- 
verted into large zoogonidangia with very much thickened walls. In 
distilled water an enormous thickening of the walls takes place. 
The vegetative cells are spherical, subspherical or ellipsoid, 65- 75 fj. in 
diameter, with a wall of fairly uniform thickness consisting of an inner 
cellulose and an outer pectic layer. They contain a wide-meshed cyto- 
plasmic reticulum with a large central nucleus and a single massive chloro- 
plast which is raised into numerous rounded lobes at its surface and occupies 
practically the whole cell except the nucleus. The cells contain oil, numerous 
granules of starch, and a variable number of pyrenoids. 
Propagation takes place by simultaneous division of the contents 
of a cell into aplanospores, preceded by numerous successive mitotic 
divisions of the nucleus of the cell. The chromatin of the resting nucleus is 
in the form of a karyosome. 
The zoogonidangia are very large, averaging 130 /x in diameter. The 
wall bears one to two rounded external pectic projections, and one to 
several internal cellulose projections which are frequently large and may be 
branched within the cytoplasm, which is correspondingly distorted. Starch, 
oil, and pyrenoids are all present. 
Zoogonidia-formation takes place by the successive bipartition of the 
contents of the mother-cell into numerous biciliate oval or pear-shaped 
bodies, which escape through a vesicle in the zoogonidangium wall. They 
develop directly into vegetative cells. 
The alga is established as an independent species on account of the very 
large size of the zoogonidangium and the great thickness and irregularity 
of its wall. 
The generic names Endosphaera, Klebs (1881), Scotinosphaera , Klebs 
(1881), and Centrosphaera , Borzi (1883), are unnecessary, since the algae thus 
named can quite satisfactorily be included within the single genus Chloro- 
chytrium , Cohn (1874), and the generic distinctions put forward by Klebs and 
Borzi are inadequate for their retention as independent genera. The new 
species described has therefore been named Chlorochytrinm grande rather 
than Centrosphaera grande. 
