18 



F. E. FRITSCH. 



South Orkneys (up. c'/t., p. 330). There is iinduubtedly sume variation in the 

 decree of separation of the cells in P. crispa, 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. crivpa lies in the 

 thickness of the walls separating adjacent cells. In P. antarcttca their thickness 

 is generally nearly equal to the width of the cell-contents, so that the latter 



DO DO 00 00 DD 00 DO 



00 pn oa 





OD DO oa 

 DD DD na 



00 QODQ 00 DD DO DO 

 a DO 



S DD 



D DD 



DO DO 00 g g 



/ L-I LJ u 



BB 



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oo 

 \ C300 O 



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A-D. Prasiola crteia (Lightf.) Menegh. ; A, part of thallus showing formation of akinetes (k); B, a normal piece of the tliallus ; C and D, 

 stages in the germination of akinetes ; E, F, Prasiola, antarctica Kiitz. ; E, normal piece of the thalflis ; F, edge of thalhis, showing 

 commencing formation of packets ; G-J, Fraxiala caloplij/lla Kiitz. ; G, two plants ; H, small part of stalk ; I, broadening out of stalk into 

 lamina ; J, edge of broad part of lamina. (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. <>'!*/'></. 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 



