HEPATICA^ 165 



single chlorophyll-corpuscle. The antherids and archegones arise 

 endogenously on the upper side of the thallus, apparently without any 

 definite arrangement, and are not protected by a perigyne. The mature 

 sporogone is an elongated dehiscent two-valved pod, provided with 

 stomates, which forces its way through a mass of tissue overarching the 

 archegone, and is known as the involucre. Within the sporange is, in most 

 genera, a solid axial columel ; the wall consists of four or five layers of 

 cells ; the rest of the contents, developed from the archespore, becoming 

 the mother-cells of the spores and elaters. Except in some species of 

 Anthoceros (L.) the elaters are of simpler structure than in the other 

 Hepaticas, having no spiral bands. Anthoceros possesses peculiar 

 cavities on the under side of the thallus, opening by slits or fissures, 

 which are regarded by some authors as stomates, by others as mucilage- 

 receptacles. Filaments of Nostoc, which have found their way into 

 these cavities through the slits, cause peculiar changes in them, and 

 have been mistaken for endogenous gemmae. The genus Anthoceros is 

 of much interest from the fact that the sporophyte-generation shows a 

 greater vegetative energy than is usually the case with Muscinete; 

 growth continues at the base of the sporange, and new spores are formed 

 there after those at the apical portion are already mature. 

 Principal genus : — Anthoceros (L.). 



Literature. 



Leitgeb — Die Anthoceroteen, 1879. 



Order 4. — Ricciace^. 



The Ricciacese are regarded by Leitgeb as forming a connecting link 

 between the Jungermanniace^ and the Marchantiacese ; but in some re- 

 spects they are simpler in their structure than either of these orders. The 

 thallus is usually flat, and branches dichotomously ; it floats on water or 

 roots in the soil. In Riella (Mont.) it is submerged and erect, and has 

 the appearance of a ring forming a continuous spiral round an axial stem. 

 It is always destitute of stomates, but is provided with internal air- 

 cavities, and with rudimentary foliar organs among the rhizoids. The 

 antherids and archegones are not, as in the Anthocerotes, endogenous^ 

 but are developed from young superficial cells of the upper surface, 

 which grow into papillae and become overarched, in the course of their 

 development, by the surrounding tissue. Both antherids and archegones 

 are enclosed in an involucre formed in this way; the antherids are 

 sessile, the involucre sometimes constituting an elevated neck above 

 them. In Riccia (L.) the archegones are ultimately buried in the 



