THE LIVERWORTS OR HEPATICS 



515 



cells each divide into four spores, while the outer cells become some- 

 what thickened to form a protective case or capsule (Fig. 338 Q, R, H) . 

 At the same time the basal part of the arehegonium grows apace and 

 may become so thickened as to give additional protection to the 

 spores o\'er the winter. When thus developed it is termed a calyp- 

 tra.^ The spores are set free in spring by the breaking down of 

 the coverings about them, and they germinate by producing a row 

 of cells of which the apical one finally develops a thallus like that 

 already described. We have thus in Riccia quite as evident an 

 alternation of generations as we found in Coleochajte, both the 

 gametophyte and the sporophyte being somewhat more highly de- 

 veloped. 



Fig. .339. — Crystahvorts. A-C, Riccia glauca (-;"): ^'1. young antheridium; 

 St, stalk. B, .same, older. C, same, still older, showing the many cells, 

 in which motile gametes (spermatozoids) are produced. D, ripe an- 

 theridium of R. minima (^1=-); e, outer cells of thallus; I, air-spaces. 

 E, R.. citiata (~;i), growing-tip cut vertically to show the terminal 

 cell (s) which by its successive divisions produces all the rest of the 

 plant, the pseudo-leaves (b'-ft"") which project from the lower surface 

 of the thallus and hold water for it, and archegonia, very young (a') 

 and full grown (a"), ready for fertilization. (Waldner, Kny.) 



Both generations are still more highly developed in the umbrella- 

 liverwort (Marchantia, Figs. 340-342), a common species growing on 

 the earth in moist localities. The spores germinate much as in 

 Riccia, but the thalli are always bisexual. At first, however, both 

 forms are essentially alike and resemble a brood-lobed Riccia. From 

 the under side arise numerous unicellular pseudo-roots and many 

 scale-like pseudo-leaves. On the upper surface are often formed 

 numerous brood-bodies of the form shoAvn in Fig. 342, which are 

 produced at the bottom of little cups the whole suggesting a minia- 

 ture nest full of eggs. By this peculiar form of vegetative reproduc- 

 tion the gametophyte is rapidly multiplied ; for as soon as a brood- 

 1 Ca-lyp'tra < Gr. kalypira, a veil. 



