1909] Collins,— Notes on Monostroma 23 
NO'TES ON MONOSTROMA. 
Е. S. QOLLINS. 
THE genus Monostroma, as proposed by Thuret,' included only 
those species of the older genus Ulva that had a single layer of cells, 
quasi-independently located in a gelatinous membrane. ‘Those 
forms with a single layer of cells, arranged parenchymatously, the 
same as the double layer in Ulva, in the restricted sense, were included 
in Enteromorpha. Under the name of Enteromorpha  Grevillei 
Thuret included Ulva Lactuca Agardh,? and the species of the same 
name of Greville? neither of these being the U. Lactuca Linnaeus.* 
Le Jolis,’ extends the genus Ulva to include Enteromorpha, and the 
species in question appears as U. Стео: ет (Thur.) LeJolis. Wittrock,® 
gave the genus Monostroma the extension that it has since held; to 
include all the Ulvaceae with a single layer of cells, arranged as a 
membrane, whatever the texture of the latter. ‘The species in question 
here appears as Monostroma Greville? (Thur.) Wittrock. Both Le 
Jolis and Wittrock gave the references to Agardh and Greville in the 
synonymy. J. G. Agardh” appears to have been the first to point 
out that it was by no means certain that the plants mentioned by the 
elder Agardh and by Greville were identical, and though he gave the 
distinctions with considerable detail, his views do not appear to have 
been accepted by later writers. That there are two forms, quite dis- 
tinct in their typical appearance, though possibly intermediate forms 
may be found, seems to the present writer to be the fact. Both occur 
on the New England coast, and both have been distributed in the 
Phycotheca Boreali-Americana; M. Grevillei as No. 15, M. Lactuca 
as No. 1271. Both are at first saccate, but the sac in M. Grevillei 
is nearly globular, in M. Lactuca more elongate; in the former species 
it soon splits into broad segments of irregular shape; in the latter into 
long, sublinear laciniae, often with a stipe-like base; these laciniae 
1 Note sur la synonymie des Ulva Lactuca et latissima L., etc. Mém. Soc. Sci. Nat. 
de Cherbourg, Vol. II, p. 29, 1854. 
? Sp. Alg., Vol. I, p. 409, 1822. 
3 Algae Britannicae, p. 172, 1830. 
4 Sp. Plantarum, Vol. II, p. 1163, 1753. 
5 Liste des algues marines de Cherbourg, p. 37, 1863. 
6 Forsók till en monographi ofver algsligtet Monostroma, 1866. 
7 Till Algernes Systematik, VI, Ulvaceae, Lunds Univ. Arsskrift, Vol. XIX, p. 101, 1882. 
