the young plants in Oedogonium. 473 
There is only a slight constriction at the point at which the 
colourless root-end goes over into the chlorophyll-containing 
part of the plant ; at this point, coinciding almost with the 
former position of the cilia,, I very frequently saw a ring 
of brown matter extending right round the cell (r in Fig. 
25, m ). 
I found considerable numbers of young plants of Oed. 
cardiacum with this type of base floating on the surface of 
the water, and most of them exhibited a striking peculiarity. 
I found that each of these was in intimate connexion with an 
air-bubble of variable size. The connexion was not alone 
a mere cohesion, but a closer examination showed that the 
otherwise spherical air-bubble was drawn out to a distinct 
point of attachment, coinciding usually with the ring of brown 
matter, mentioned above (cf. Fig. 27 , h ; a is the bubble). It 
would thus appear as though there were some connexion 
between the presence of the air-bubble and this brown matter, 
for the two nearly always occurred side by side. The curious 
shape of the bubble suggests its having been formed on 
the plant itself, which was by this agency enabled to float 
to the surface of the water 1 . All my attempts to elucidate 
this point have as yet proved unsuccessful, as the bubbles 
break up soon after the plant is removed from its floating 
position. The substance forming the brown ring is un- 
doubtedly ferric oxide or some ferric salt. The same is 
very commonly found forming a coating on the basal disc 
of this and other species of Oedogonium. It is often present 
in considerable quantity at places where young plants of this 
genus are attached to other filamentous Algae. If treated 
with a solution of potassium ferrocyanide, to which a trace 
of hydrochloric acid has been added, this brown substance 
is dissolved, and in its place a precipitate of Prussian blue 
is formed (cf. Zimmermann, ’92, p. 66 ). 
1 Cf. also Chodat, ’02, p. 92 : ‘ C’est ainsi qu’on rencontre tres commun&nent 
les Ulothriciacees, les Palmellacees, les Confervac^es, les Oedogoniees et les 
Conjugees constituant des echeveaux denses de filaments suspendus . . . par les 
bulles d’oxygene qu’ils exhalent an soleil. . . .’ 
