Notes. 
652 
of successive ring formation in Oed. cardiacum , Wittr. ; in . this case, however, the 
annular thickening had developed in the normal manner, and a certain amount of 
stretching of the rings had taken place, so that they were quite distinct from one 
another (cf. loc. cit. Fig. 27 a ). — The abnormal tip described in the present note is 
certainly due to unfavourable conditions. The material has been inside the same 
glass vessel for a period of nearly two years, and, owing to the slow evaporation of 
the water, large numbers of the young plants, attached to the sides, have been 
exposed for several months. Most of them, all the same, present a relatively healthy 
appearance (cf. below, however), and, owing to the vessel being closed above by 
a glass disc, they are always in a damp condition by virtue of the evaporation and 
condensation of the water below. Still the conditions under which they live are 
distinctly aerial, and this has probably led to the terminal cell losing its capacity for 
division. In the water at the bottom of the vessel a rich growth of Oedogonium has 
developed in the last months, and these filaments, although presenting the same type 
of basal cell, do not show this peculiar cap at the apex. Ultimately these caps drop 
off and the exposed apex of the filament is generally somewhat pointed (cf. Fig. 61 f), 
a contrast to the young stage, in which it is mostly quite rounded off. Even below 
the accumulating cap-substance the terminal cell of the filament can be seen acquiring 
this pointed apex (cf. Fig. 61 a and c). 
This cap-like structure seems to afford a good means of judging of the structure 
of the normal thickening of the Oedogonium- cell. A number of theories have been 
put forward as to its mode of origin and ultimate structure, and it is unnecessary here 
to consider them in detail. According to Wille 1 the ring consists of a short layer of 
cell-wall substance, containing a greater percentage of water than the inner layer of 
the cell-wall, between which and the cuticle it is formed by intussusception. Hirn’s 2 
observations tend to show that the inner portion of the ring consists of a mucilaginous 
mass, surrounded by an internal layer of cellulose ; according to him, however, ‘ ist 
die den Schleim umgebende, peripherische Ringschicht nicht etwa eine Falte der 
urspriinglichen Mutterzellwand, sondern wird, nachdem der Protoplast zuerst den 
Ringschleim ausgeschieffen hat, als eine innere Membranschicht angelegt, die ober- 
und unterhalb des Ringes mit der alten Membran dicht verwachsen ist’ (loc. cit. p. 7). 
Hirn supports this theory by observations made on cells in which plasmolysis was 
induced by means of an 8 % solution of cane sugar ; under these circumstances the 
protoplast merely excretes a ring of mucilage without the formation of the enveloping 
cellulose-layer. It is quite eas^..^) make out the two portions of the ring, indicated 
by Wille and Hirn, without the use of staining reagents, in any actively dividing 
Oedogonium- cell ; as to the mode of origin, I incline to the belief that Wille’ s theory 
is more correct. It is not easy to understand how the peculiar cap-structure, de- 
scribed in the present note, could have originated in any other way. The darker 
substance, which makes up the main mass of the cap, is evidently equivalent to 
Wille’s water-containing layer and Hirn’s mucilage-layer. The distinct stratification 
of this mass indicates its periodic deposition between the outer cuticle, which surrounds 
the whole and the well-marked inner layer of the cell-wall, which forms the internal 
1 Ueber die Zelltheilung bei Oedogonium. Pringsh. Jahrb., vol. xviii, 1887, p. 444. (‘Der 
Ring ist also eine kurze wasserreichere Schicht in der Membran.’) 2 loc. cit., pp. 6 and 7. 
