448 FREDERICK KEEBLE. 
in vacuole-like bodies termed physodes. ‘The contents of the 
physodes blacken with osmic acid, and give the vanillin 
reaction for phloroglucin or tannin. According to Koch, 
(1896) who denies the presence of tannin, the physodes 
contain a colloidal substance formed from a polysaccharide 
and also a nitrogen-containing body. 
In Dictyota, Hunger (1902) states that a carbohydrate 
occurs in the outer, and a glucoside in the inner, layers of 
cells, and that these substances disappear from the cells of 
dark-kept plants. The assimilate of the Diatomacee is 
stored generally outside the chloroplast in the form of oil, 
(Oltmanns, 1905). Dinobryon, a member of the Chryso- 
monadinee, contains white balls of unknown nature termed 
by Klebs (1892) leukosin. In other members of this group 
Meyer (1897) describes a fatty oil as the reserve substance. 
The nature of the reserve-form of the assimilate of the 
Zooxanthelle occurring in Radiolaria has been investigated 
by Haeckel, Miller, Brandt, and others, but the conclusions 
are not very convincing. According to Haeckel these yellow 
cells give a blue reaction with iodine (Cienkowski, 1871), 
whereas Miiller obtains a brown reaction, deepening on the 
application of sulphuric acid. Brandt (1885), in his well- 
known monograph on the Radiolaria, states that the assimi- 
late lies in the chloroplast (chlorophyll body), and is of two 
kinds. One form is starch, consisting of fine granules, 
which occur as a thin ring about a large vacuole. These 
bodies are not doubly refractive, and are described as hollow 
starch grains. The other form of assimilate consists of 
doubly refractive, fine, irregular, red-violet granules, which 
undergo no colour-change with iodine. ‘They are not 
numerous in diffuse light, but increase in numbers when 
animals are exposed to bright light for half an hour. 
With reference to these various observations several points 
may be noted. First, the iodine coloration, brown or blue, 
must not be taken to indicate the certain occurrence of 
starch. Yellow algal cells such as Zooxanthelle are rich in 
carotin, which substance gives a green or blue-green colour 
