i6o 



SECOND GROUP. MUSCINEAE, 



B 



rhl 



conferva-like cells grow out containing chlorophyll (Fig. no, chl), while the rest of 

 the tissue is without chlorophyll. 



The stomata are in some species bounded by several concentric circles of cells, all 

 lying in the plane of the upper surface of the thallus, which is formed of one layer of 

 cells ; this is the case in Fegatella (Fig. 112). In Preissia and Marchantia on the 

 other hand the orifice is a circular canal formed by several tiers of cells (Fig. 110), and 

 a similar construction is found in the stomata on the sexual shoots, and even in species 

 of the Marchantieae which have only simple stomata on their thallus. The air- 

 chambers are formed in much the same manner as those of the previous sub-division. 

 Small pits are formed behind the apex (Fig. 112, Ik), which are separated from each 

 other at first by one cell only. These pits become much deeper and broader and the 

 adjacent parts grow up over them. The cells which surround the narrow opening to 

 these cavities on the outside divide in a plane parallel to the surface, and thus produce 



the peculiar canal-like stomata. 

 Then in Marchantia, Preissia, 

 and others the segmented fila- 

 ments containing chlorophyll 

 shoot out from the bottom of 

 the cavity ; they are absent in 

 the genera Sauteria and Clevea. 

 The rest of the tissue is with- 

 out chlorophyll and consists of 

 long, horizontally elongated cells 

 without interstices (Fig. in), 

 and often with broad pits on 

 their walls. In Preissia^ are 

 found strings of elongated uni- 

 formly thickened cells with very 

 dark coloured walls. The mu- 

 cilage-organs are peculiar ; and 

 are most highly developed in 

 Fegatella, where longitudinal 

 rows of cells are transformed into 



FIG. in. Transvers section through the thallus of blarchantia polymorpha, mUCllagC-Canals by the thicken- 

 A middle portion with scales b and rhizoids /; on the under side, magn. 30 times. ft! -11 11 ,-! fV. 



B margin of the thallus more highly magnified ; / colourless reticulately. ing Ol tllC CCll-WallS and tfieir 



thickened parenchyma, o epidermis of the upper side, chl the cells containing pnnvprQinn illfn milfilacrp thp 

 chlorophyll, sf stoma, s partition-walls between the air-chambers, it lower tl S c > < ult 



epidermis with dark-coloured cell-walls. Cell appearing tO be filled with a 



strongly refractive jelly. Single 



cells of this kind are found in the thallus and the sexual shoots of others of the 

 Marchantieae 2 . 



The sexual organs of the Marchantieae are dioeciously or monoeciously disposed, and 

 there is considerable variety in the construction of the shoots which bear them. In 

 Clevea hyalina and Sauteria alpina the antheridia appear singly on the dorsal side of 

 ordinary shoots, as in Riccia. In Targionia the archegonia are formed on the growing 

 apex, which can continue to grow if fertilisation is not effected. The group of arche- 

 gonia is inclosed by the growth over it of the dorsal and lateral tissue of the thallus. 

 The antheridia and archegonia of many species of Flag ioch asma and the antheridia of 

 Fimbriaria and Peltolepis are placed several together one behind another on disc- 

 shaped receptacles on the dorsal side of the thallus. But the male and female 

 receptacles in Fegatella, Preissia, Marchantia and Dumortiera are composed of an 

 entire branching-system. In the male receptacles of Marchantia for instance (Fig. 



1 Goebel, Zur vergl. Anatomic d. Marchantieen (Arb. d. Bot. Instit. in Wiirzburg, II Bd.). 



2 [Prescher, Die Schleimorgane der Marchantien (Sitz. d. k. Acad. d. Wiss. Wien, 1882).] 



