Hydrodictyon tUrictdatum. 621 
pyrenoid in Spirogyra and Zygnema whose points project be- 
tween the parts of the surrounding starch-layer. Chmielewski 
insists that the pyrenoid is a permanent cell-organ always 
arising by the division of a pre-existing pyrenoid, a view 
previously suggested by Schmitz and Strasburger 1 ; still 
Schmitz also described the origin of pyrenoids in Nemalion , 
de novo — and Strasburger described the disappearance of 
the pyrenoids prior to the formation of the swarm-spores in 
Cladophora . 
In his paper on the formation of the reproductive cells of 
Hydrodictyon Klebs 2 attempted to establish, by certain ex- 
perimental culture-methods, a difference between the so-called 
pyrenoid-starch and the stroma-starch. But in this work 
Klebs, like his predecessors, failed to find the real genetic 
relation between the pyrenoid and all of the starch. 
From the brief resume given above it may readily be seen 
that there has been very little contributed towards the solu- 
tion of the problem as to the nature of the relation of the py- 
renoid to the formation of starch. This' has been apparently 
due to two causes, the failure to find stages showing active 
starch-formation, and inadequate methods of treatment in 
studying the early and most important stages in the process. 
The material I have used was fixed in either Merkels fluid 
or in one of the two iridium chloride and acetic acid mixtures 
whose formulas I have already published in another con- 
nexion. The material was embedded in paraffin and cut on 
a microtome into sections of from three to six /jl in thickness. 
The triple stain of Flemming gives a very clear differentiation, 
staining the pyrenoid bright red and the starch blue, while 
the surrounding cytoplasm is stained orange 3 . 
The general structure of the Hydrodictyon cell has long 
Centralbl., Bd. lxix, p. 277. Die Pyrenoide. Bot. Centralbl., Bd. lxxvii, 
p. 108. 
1 Zellbildung u. Zelltheilung. 
2 Fortpflanzungszellen bei Hydrodictyon utriculatum , Roth. Bot. Ztg., 
1891. 
3 A more detailed account of the method of procuring and treating the material 
will be published later, in another connexion. 
