from the same locality to found any characters upon its gradations. 
By older writers Ulva latissima was either entirely confounded 
with U. dactuca, or else was regarded as merely a variety of it. 
The distinctions are well poimted out by Dr. Greville, and are as 
visible in the young as in the full grown plant. Ulva latissima 
is, at all stages, a flat membrane, and in drying scarcely adheres 
to paper. U. dactuca is, at first, a closed sac, which soon bursts ; 
it then exhibits a torn membranous frond, of a much more deli- 
cate substance than U. /atissima, and of a paler colour; and in 
drying, it closely adheres to paper. 
Lightfoot and succeeding authors tell us that U. Jatissima, 
under the name of Oyster-green, or Green-Sloke, is brought to 
table both in England and Scotland, used in the same manner 
as Porphyra laciniata, the true Laver or Sloke. I have never 
seen it so used. Lightfoot further says that ‘the Icelanders 
ascribe to it an anodyne virtue, and bind the leaves about the 
front and temples to assuage the head-ache in fevers, and to pro- 
cure sleep ; but the use of it in these intentions is supported by 
no good authority.”— FV. Scot. p. 971-2. If it have any effect in 
such cases, it probably arises from the cooling influence of the 
moisture retained in the leaves. 
Fig. 1. Unva Latissima ; a frond:—of the natural size. 2. Portion of the 
surface. 3. Section of the frond :——highly magnified. 
