1909] Collins,— Notes on Monostroma 25 
and the same species, we had better take as a species every form that 
can be described plainly enough to be recognizable, than form species 
of artificially grouped forms." While this last suggestion goes too 
far, something near it may be temporarily admissible until we have a 
life history of each species, from the spore on. In the meantime it 
is almost as hard to draw sharp lines between M. undulatum Wittr., 
M. pulchrum Farlow and M. Grevillei, as they occur on the American 
coast, as it is between M. Grevillei апа M. arcticum, as we under- 
stand them; for the sake of clearness it has seemed better to the 
writer to make more specific distinctions than Rosenvinge found 
expedient; in the matter of M. Greville? and M. Lactuca, it is hoped 
that the new character, in the fertile frond, will render this distinction 
more acceptable. As this very distinct form of the fertile cell really 
amounts to the formation of a specialized sporangium, it would seem 
to place this species at the head of the genus. 
At page 63 of Jónsson's work, he refers again to the writer's paper on 
the Ulvaceae, calling attention to Rosenvinge's note! that the cells of 
M. fuscum (Post. & Rupr.) Wittr. contain two chromatophores, one 
at each end; adding as a footnote, “F. S. Collins (The Ulvaceae etc.). 
does not at all mention this important character neither in the descrip- 
tion of the species nor in the description of the genus Monostroma.” 
The writer has since made a careful examination of fresh material, 
collected at Revere Beach, Massachusetts, the locality at which were 
collected the specimens distributed as Phyk. Univ., No. 64, and P. B.- 
A., No. 715. In every instance a single chromatophore was found in a 
cell. It is, of course, possible that the Greenland plant is different 
from the plant of the New England coast, but this is hardly likely, as 
the figure in Wittrock, l. c., Pl. III, fig. 11, shows a perfectly uniform 
chromatophore, quite like the Revere Beach plant; and this was 
drawn from a specimen collected in Norway. A more probable ex- 
planation is suggested by the fact that in dried specimens of green. 
algae the contents of the cells shrink, and the remains of the chroma- 
tophores tend towards the ends, leaving the middle apparently empty; 
this is very conspicuous in plants with large cells, like Chaetomorpha 
Melagonium (Web. & Mohr) Kützing. 
M. orbiculatum Thuret,? was not mentioned in the writer's paper on 
Ulvaceae, previously referred to, but what appears to be this species 
1 Gronlands Havalger, Meddelelser om Gronland, Vol. III, p. 940. 
2 Mém. Soc. Sci. Nat. de Cherbourg, Vol. II, p. 388, 1854. 
