68 BRITISH MARINE ALG. 
axis or central portion of the stem is composed of elongated interlacing 
fibres, imbedded in gelatine; the outer margin is made up of horizontal 
or radiating tufted branching filaments, among which the dark olive 
coloured spores are produced. The name is from the Greek for “ middle” 
and “‘ viscid,’’ in reference to the viscid or glutinous nature of the axis. 
Mesogloia vermicularis is the common species found all round our coasts. 
It grows on rocks and in tide pools, and is sometimes cast ashore of large. 
size. The fronds are irregularly and usually much branched, being set with 
numerous ramuli, all of which, like the stem and main branches of the 
plant, are flaccid and slimy, and singularly worm-like, hence the specific 
name. The colour is a dark yellowish olive, which it generally retains in 
drying. WM. virescens, a main branch of which is represented at Fig. 71, 
is, in many respects, similar to the former species, but may be known by its 
much lighter colour, which inclines more to a green than an olive tint, 
especially in drying, when it invariably turns to a pale yellowish green. 
These curious plants are very variable in size. The former sometimes 
attains a length of 2ft., but the latter I have never known to exceed 12in. or 
l5in. The species M. Grifithsiana is rare. It was named after the late 
Mrs. Griffiths, of Torquay, who discovered it. The fronds rarely exceed 
a foot in height, and are much more slender and less copiously branched 
than the two species already described. It is said to be found on the West 
of Ireland, and although it is decidedly rare on the English shores, I have 
taken several beautiful specimens near Plymouth, on different occasions. 
All the species of Mesogloia, when displayed on paper, must be allowed 
to dry for several hours before the slightest pressure is attempted. 
At the head of the fleshy or cartilaginous seaweeds is placed the curious 
plant known as Leathesia tuberiformis (Fig. 72), named in honour of Rev. 
Mr. Leathes, an eminent naturalist. This singular marine production has 
exactly the appearance of a mass of distorted tubers variously heaped 
together, suggesting the not inappropriate name of ‘‘ sea potatoes.’’ In 
early growth the roundish lobes of this alga are solid, or filled with densely- 
packed cotton-like fibres, but as they advance in growth they become 
hollow and break away from the rocks or seaweeds on which they grow. 
The structure of this tuberous mass is very remarkable, but it would require 
a large series of diagrams to illustrate a description of its composition. 
The illustration gives a good general idea of its form as it is found in 
various stages of growth on rocks or attached to other seaweeds. L. crispa 
is a small and somewhat insignificant species, parasitic on Chondrus 
crispus. It was discovered not many years since by a naturalist in 
Scotland. L. Berkeleyi, though not so abundant as the type of this genus, 
is not uncommon, but being of a dark brownish olive, and growing close 
to the surface of submarine rocks, it frequently escapes notice, or when 
found is too often rejected on account of its generally unattractive appear- 
ance. When specimens of these fleshy plants are desired for the herbarium, 
portions of the young plants should be selected, and after being cleaned 
from sand or other foreign matter, the mass should be placed on mounting 
