18 F. E. FRITSCH. 
South Orkneys (op. cit, p. 3830). There is undoubtedly some variation in the 
degree of separation of the cells in P. erispa, although it does not appear ever 
to attain to the pronounced separation typical of P. antarctica. Since seeing the 
typical form of the latter species in the present material, I have realised that 
it was not present in the South Orkneys material at all. 
The most pronounced difference between P. antartica and P. crispa lies in the 
thickness of the walls separating adjacent cells. In P. antarctica their thickness 
is generally nearly equal to the width of the cell-contents, so that the latter 
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A-D. Prasiola crispa (Lightf.) Menegh. ; A, part of thallus showing formation of akinetes (k); B, a normal piece of the thallus; C and D, 
stages in the germination of akinetes; E, F, Prasiola antarctica Kiitz.; E, normal piece of the thallus; F, edge of thallus, showing 
commencing formation of packets; G-J, Prasiola calophylla Kiitz. ; G, two plants ; H, small part of stalk ; I, broadening out of stalk into 
lamina ; J, edge of broad part of Jamina. (G, magnified about 5 times ; C and D, x 700; all other figs., x 500.) 
appear remote from one another (text-figure E). The arrangement of the cells in 
groups separated by wide interspaces is thereby rendered far less distinct, and in 
parts of the thalli from Mt. Terror was quite unrecognisable. As a consequence 
the thalli present an even more uniform appearance under the microscope than 
obtains in P. crispa. In the material from Mt. Terror there also appeared to be 
a tendency for the cells to be squarer in surface-view than is usually the case in 
P. crispa. The margins of the thalli were not as irregular as in the latter species, 
and the size of the whole plant was appreciably less; some of the thalli in my 
