244 PHYLUM VIII. BRYOPHYTA 
the top and surrounding the row of canal cells, but later 
open with a continuous passage to the egg (owing to the 
dissolution of the canal cells). In fertilization which 
takes place in water, the sperms pass down the tubular 
neck to the egg below. 
425. Mossworts are of small size, rarely exceeding 10 or 
15 centimeters in height. They generally prefer moist 
situations upon the ground, or on the sides of trees or 
rocks. All told there are somewhat more than 16,000 
species. ‘Two classes may be distinguished, as follows: 
Mostly bilateral, often thalloid, creeping gametophytes, 
usually with splitting sporophytes, and mostly having 
Chater os Orel ee ces eae poe eries Class HEPATICAE. 
Multilateral, leafy-stemmed, mostly erect gametophytes, usu- 
ally with circularly dehiscing sporophytes, and without 
GAGORR G 6.6550 2's nk Actaeete Bieta en Class Musct. 
Ciass HEPATICAE. Liverworts 
426. In the lower Liverworts the gametophyte is a flat, 
expanded thallus of parenchymatous tissue, and this 
gradually differentiates into a leafy stem as we pass to 
the higher forms, but in all cases the plant body has two 
distinct and well-marked surfaces, an upper and an under 
one, the latter bearing the root-hairs (rhizoids) by which 
the plant is fixed to the ground. About 4000 species are 
known. 
427. Among the simplest of the Liverworts are the 
little round, flat Riccias (Riccia) which grow on wet earth 
or even float on the water. In the upper surface of the 
loose green tissue are the sunken antherids which pro- 
duce biciliated spiral sperms. In a similar manner the 
archegones are sunken in the upper surface. After fer- 
tilization the egg develops into a globose cellular body 
a he ee cmt 
