aia by breaking up into ated Bek Auden foe when % 
these spherical cells become closely crowded. together by 
the gradual evaporation of the fluid, they coalesce into a_ 
pellicular stratum, the individual globules assuming a “poly- 
gonal form in consequence of their mutual pressure. This ~~ 
latter form was at one time described under the name Zzm- 
nodictyon Remurianum, Al\gee are rarely true parasites, 
although they very commonly inhabit the surface of other 
plants ; they much more often obtain their food by direct 
assimilation. They may be classified according to their 
habitat into Freshwater and Marine Alge. The former are 
mostly green, and are found plentifully in any stagnant 
water or ditch in the spring and summer, and not unfre- 
quently contribute, by their process of vegetation, to the 
removal of substances decaying in the water. The red, 
- green, and brown marine Algz are larger and of much greater 
beauty ; some of these live only in the breakers, others only 
on the quiet bed of the ocean. ‘They very often occur in— 
great masses; the largest of these is the ‘ sargasso sea,’ which 
“occupies several thousand square miles in the Atlantic be- 
tween 19° and 34° N. iat. and 34° and 36° W. long., the 
surface of the sea being covered with detached sterile masses 
of the ‘ gulf-weed, Sargassum natans (Fig. 387). Sarcina or 
Merismopedia ventriculd is commonly found in the gastric 
juice of man ; and it is still an undecided question whether 
these cube-shaped cells united together in strings are of 
pathological character ornot. The number of types included 
in Algee is not remarkably large; but that of the individuals 
which are collected in masses 1s enormously great. | 
The gelatinous substance of the cell-walls gives to | 
several kinds of Algze the property of being used as articles 
of diet, such as the species of Zaminarza and Ulva (green 
laver) on the coasts of Scotland and Ireland, and the ‘carra- — 
geen moss’ which is obtained from Spherococcus crispus and — 
mammillosus. ‘The ashes of the larger marine Algee were at 
one time largely employed, as kelp, in the manufacture of — 
