BBTOPSTTA. 



151 



of trees. Besides the sexual r'eproduction by means of 



archegonia and antheridia, they 



multiply extensively in a non-sexual 



manner ; namely, by the production 



of peculiar buds, called gemma 



(Fig. 263, gem). These, in the 



common Liverwort {Marckantia), 



are little cellular bodies, developed 



in cups, ou the upper surface of 



the thallus. When the gemmae are 



full-grown, they fall to the ground, 



and grow directly into new plants. 



The stomates in these plants are 2«3, 



not of the ordinary kind found in higher groups ; instead 



of being surrounded, as there, by two guard-cells, there are 



sixteen (or more) cells, in four (or more) superposed layers, 



encircling the orifice, which leads into a large air-cavity 



below the epidermis. In this cavity are branching rows 



of cells, which contain the chlorophyll-masses (Fig. 264). 

 2. Musci. This group includes the Sphagnums and 



the true Mosses. The plants (Fig. 262) have stems, 



with sessile leaves and articu- 

 lated root-hairs, or rhizoids ; the 

 leaves are composed of a single 

 layer of cells, and may, or may 

 not, have a midrib. The st^ms 

 may have an outer, thickened 

 layer, or layers (imperfect scle- 

 renchyma) ; and within, either 



simply thin-walled parenchyma, or an axial bundle of 



very narrow, thin-walled cells — imperfect fibro-vascular 



Fig. 263. A portion of a Liverwort, with the gemmae in cup-Ukc cavities. Fig. 

 264. Section of a frond of Liverwort, showing the stomate (si) and the air-cavity 

 (a) below, containing the cells which have the chlorophyll (cU). 



264 



