FRESHWATER ALGAAS. il 7 
production of packets for purposes of propagation is not confined to the margin of the 
thallus, as Wille (Nyt Mag. f. Naturvidenskab, x]l., 1902, p. 215) describes it, but 
can take place anywhere. 
In the above-mentioned paper of Wille’s a number of reproductive stages of 
another kind are described and figured (op. cit., p. 216, Tab. IIL. figs. 13-19); these 
are supposed to be the products of unicellular akinetes produced from the margins 
of the thallus (¢f Gay, Recherches sur le développement et la classification de 
quelques Algues vertes, Paris, 1891, fig. 130). Stages like those shown in Wille’s 
figs. 13-15 were common not only in the material from Cape Adare, but more or less 
isolated among other Algze from several other localities (notably from the Gap pond). 
There can be no doubt that these stages arise from large unicellular akinetes, as such 
were frequently observed in the mature thalli (text-figure A, 4). These akinetes are 
however by no means confined to the margin of the thalli, but can arise anywhere. 
They are generally more or less separated from one another, the surrounding cells 
being often quite irregularly arranged, pale in colour and apparently in a moribund 
condition (text-figure A). The akinetes are spherical and vary in diameter between 
10 and 14; they have a thick membrane. Division of the contents of the akinete 
(text-figures C and D) does not appear to take place until it is liberated by the decay 
of the surrounding thallus, but there may be exceptions to this rule. 
I have no doubt that Wille is right in regarding these cells as sporangial, as the 
irregularity of arrangement of the products of their division excludes the possibility 
of their being the beginnings of a new thallus. Wille thinks that the products 
(his aplanospores) on liberation give rise to the fMormidiuim-stage. While this may 
frequently be the case, there seems to be indirect evidence that they may sometimes 
give rise straight away to the characteristic Prasiola-packets. The abundance of such 
packets on the Phormidium-sheets from many localities is scarcely explicable on any 
other hypothesis. There are no mature Prasiola-thalli, from which these packets 
could have been derived, at hand in these localities, whereas the dividing akinetes 
are not uncommon. 
The filaments of the Hormidium-stage from Cape Adare measured 9-11, in 
diameter. 
12. PRASIOLA ANTARCTICA. 
(Text-figures E and F.) 
Prasiola antarctica Kiitz., Spec. Alg. (1849), p. 473; Tabul. Phycol., v., Tab. 40, fig. 4 ; Rabenhorst, op. 
cit., iii. (1868), p. 311. 
fab.—Growing on stones, Mt. Terror, January 22nd, 1902. 
It is with some degree of diffidence that I refer the form from Mt. Terror 
to a species distinct from P. crispa, as I do not feel quite convinced that the 
differences are of specific value. P. antarctica might perhaps be regarded merely 
as a variety of P. crispa, as 1 advocated in my paper on the Algae of the 
. 
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