248 FIRST FORMS OF VEGETATION. 
species, Zetraspora lubrica, forming irregular 
masses of considerable extent, and exceedingly 
lubricous, in gently running water, has its fruit, 
consisting of minute granules imbedded in the 
fronds, loosely arranged in fours. The first stages of 
all these fresh-water representatives of the marine 
Ulve, are in all respects simple conferve ; but 
the cells at the extremity of the filaments divide, 
and by repeated division, these filaments are 
laterally expanded, until they form a plain leaf- 
like frond, as in Ulva, or close all round after they 
have expanded, until they produce a tube or sac 
as in Enteromorpha. 
One of the most singular of the confervaceous 
alge is the Botrydium granulatum. It grows on 
the ground in moist shady situations in spring 
and autumn, and is perhaps more frequent than 
is supposed, its minute size causing it to be over- 
looked. It consists of a number of green vesicles 
of the size of a pin’s head, aggregated together, 
and sunk, as it were, into the soil, the whole 
bearing a close resemblance to a miniature branch 
of unripe grapes, whence the name. Under the 
microscope, each vesicle appears filled with a 
watery fluid containing minute granules, which 
escape when ripe by an opening at the top; 
in dry weather the upper part collapses, sinks 
in, and becomes cup-shaped. The vesicles are 
