474 Fritsch . — The Structure and Development of 
In the other species examined the above-described feature 
was not observed, although the floating individuals are fre- 
quently found aggregated in large numbers (being then often 
almost radially arranged) round a single large air-bubble, 
which, however, exhibits a perfectly circular outline. The «• 
floating plants form a bacteria-like scum on the surface of 
the water, and large numbers may be obtained by dipping 
the tip of the finger into the water and conveying a drop 
on to a slide. 
It is unnecessary to mention all the variations in the types 
of basal-end observed in Oed. capillare ; this species seemed 
the most variable of all in this respect. The simple rhizoid 
not infrequently divides irregularly after some time, thus 
giving rise to a structure like that figured by Poulsen (’ 79 , 
Tab. i, Figs. 2, 3, 4, and 6) ; also Cohn (’ 54 , Tab. 20). I 
occasionally saw the rhizoid of a young plant, which had 
attached itself to another (empty) one, divide up into a 
number of small processes, each of which twined itself round 
the substratum ; somewhat similar cases were also found in 
the species from the river Severn (Fig. 25, /). Apically the 
filaments of Oed. capillare sometimes terminated in a swollen 
cell (Fig. 26, b ), the cell below then bearing a large number 
of caps, thus indicating that the terminal cell had not divided 
since its first formation. In a few cases two tips were present 
(Fig. 25,^). 
The undetermined species from the river Severn also showed 
a certain amount of variation in the structure of its root-end. 
The attaching-disc, when found here, is frequently slightly 
turned upwards round the edge (Fig. 25, i). Delicately 
branched roots are not uncommon (Fig. 25, /), and form an 
intermediate step between the basal-disc and the unbranched 
rhizoid. 
In order to complete my description of the root-ends of 
Oedogonium I must make mention of the hemispherical basal 
cells, whose curious mode of development has been recently 
worked out by Lemmermann (’ 98 , p. 504) and Scheflerle 
( 1901 ). Hirn ( 1900 , p. 15) has shown that they occur in 
