632 Timber lake. — St arch- Formation in 
involving many chemical transformations whose nature must 
be left to future investigations to determine. The fact that, 
as seems to be well established by various observers, the 
pyrenoid is of a proteid nature, and that a portion of it — at 
least in Hydrodictyon — is converted into starch, suggests that 
the process involves the breaking down of a proteid into 
a carbohydrate. Still, it is not to be thought that the sub- 
stance of the pyrenoid is merely passive in the process, for on 
that assumption it would be hard to explain the differentia- 
tion of its body into two portions, one of which is transformed 
into starch, while the other retains the original pyrenoid 
character. 
To be sure the pyrenoids themselves may totally disappear 
at certain periods in the life-history of the cell, notably prior 
to reproduction ; but it is quite probable that active cell-organs 
may disappear when their work is not immediately needed, 
and be formed anew when their activities become necessary. 
(Cf. Wilson, The Cell, p. 305, as to the centrosome.) 
Whether the pyrenoid represents an active, independent 
cell-organ whose function is the formation of starch, or whether 
it is to be thought of as a mere stage in the process of starch- 
formation whose real seat is to be found in the chlorophyll- 
bearing cytoplasm, is not certain from the facts thus far at 
hand. As pointed out above, the method of differentiation of 
the body of the pyrenoid preceding the actual formation of 
the starch indicates that the pyrenoid is more than a passive 
body representing a stage in the process. The genetic history 
of the pyrenoid itself, including its relations to the chromato- 
phore, where a differentiated chromatophore exists, or to the 
cytoplasm in such a form as Hydrodictyon , would perhaps 
throw some light on the nature of the whole metabolic pro- 
cesses resulting in starch-formation. 
In the paper previously referred to, Boubier developed the 
interesting hypothesis that the pyrenoid is comparable to the 
leucoplast of the higher plants, and that the method of starch- 
formation in it is similar to that in the latter bodies. While 
the suggestion may later prove to be a valuable one, still 
