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within the enlarged base of the leaves, those of the inner leaves filled 
with minute powdery granules, those’ ‘of the outer bane containing 
larger grains, at first cohering in fours. 
A small genus, widely spread over the greater part of the globe: fii @ 
1. I. lacustris, Linn. (fig. 1265). Hwropean Q.—A perennial, of a 
bright green, forming dense tufts under the water. Leaves narrow- 
linear, thick, and nearly terete or 4-angled, much like those of several 
Monocotyledons, varying from 2 to 6 inches long, their enlarged bases 
giving the plant often a bulbous appearance. 
In mountain pools, and shallow lakes, in central and northern Europe, 
northern and Arctic Asia, and North America. In Britain, in the moun- 
tainous parts of Scotland, northern England, Wales, and Ireland. Fr. 
summer and autumn. [I. Morei, Moore, is a variety with leaves 18 inches 
_ long, found in Wicklow.] Modern botanists distinguish as JL. echinospora, 
Durieu, a form found in our mountain lakes, often growing with the 
common one, but said to be only where the soil is peaty. It differs 
chiefly in the larger spores covered with acute tubercles instead of being 
granulate only or smooth on thesurface. A more distinct form referred 
to J. Hystriz, Durieu (fig. 1266), occurs in moist sandy hollows on 
Laucresse Common in Guernsey. The rootstock is covered, outside the 
tuft of leaves, with a number of small, imbricate, toothed or jagged 
brown scales, which are the persistent remains of old leaves, and which 
are never observed in the common under-water forms. It remains to 
be seen how far this difference may be owing to situation. 
550 THE CLUBMOSS FAMILY. 
XCII, MARSILEACEA. THE MARSILEA FAMILY. 
No true leaves. Fronds, as in Filices, proceeding from the 
rootstock and rolled inwards at the top, barren ones either 
reduced to a narrow-linear stipes, or in an exotic genus bearing 
4 digitate leaflets; fertile ones sessile or on a short stipes, 
bearing a globular or ovoid utricle, usually called an involucre, 
and formerly considered as analogous to the spore-cases of 
Lycopodiacee, but which is really the recurved fertile lamina 
with the margins united. Real spore-cases of two kinds, larger 
and smaller, as in Selaginacece, but arranged, as in F%lices, inside 
the involucre, that is, on the under surface of the recurved 
frond, in sori pained in membranous indusia, dividing the 
involucre into as many cells. 
The Order was formerly supposed to be closely connected with Lyco- 
podiacee, in which the only British genus was included in our first 
editions, but its still nearer relation to Filices has been well pointed out 
chiefly by German botanists. It contains only one genus besides the 
British one. 
——— ea ae oe 
IJ. PILULARIA. PILLWORT. 
Rootstock creeping under water, with subulate, barren fronds, almost 
solitary atthe nodes. Involucres (or fertile fronds) almost sessile on the 
