DIV. I 



BRYOPHYTA 



485 



occur at all. The epidermis on the under side of the thallus is formed of one layer 

 of cells. The tissue below the air-chamber layer is devoid of chlorophyll, and 

 consists of large parenchymatous cells, which serve as storage cells. 



Small cup-shaped outgrowths, with toothed margins, the gemmiferous receptacles 

 or gemma-cups, are generally found situated on the upper surface of the thallus over 

 the midribs (Fig. 445 &). These contain a number of stalked gemmae, flat, biscuit- 

 shaped bodies of a green colour. The gemmae arise by the protrusion and repeated 

 division of a single epidermal cell (Fig. 444) ; at maturity they become detached 

 from the stalk (at x, Fig. 444 D}. They are provided with two growing points, 

 one at each of the marginal constrictions, from which their further development 

 into new plants proceeds. On cross-section (E] they are seen to be composed of 

 several layers of cells ; some of the cells are filled with oil globules (D, o), while 



from other colourless cells rhizoids develop. 

 Cells containing oil are also present in 

 the mature thallus, and are of frequent 

 occurrence in all the Hepaticae. By 

 means of the abundantly - developed 



FIG. 444. Marchantia polymorpha. A-C, 

 Successive stages in the formation of a 

 gemma ; st, stalk-cell ; D, surface view ; 

 E, transverse section of a gemma ; x, 

 point of attachment to stalk ; o, oil cells ; 

 r, colourless cells with granular contents, 

 from which the rhizoids will develop. 

 (4-Cx275; D-Ex65. After KNY.) 



FIG. 445. Marchantia polymorpha. A, A male 

 plant, with antheridiophores and gemma-cups b 

 (nat. size). B, Section of young antheridiophore ; 

 a, antheridia ; t, thallus ; s, ventral scales ; r, 

 rhizoids. (Somewhat magnified.) 



gemmae Marchantia is enabled to multiply vegetatively to an enormous extent. 

 The dorsiventrality of the plants developed from the gemmae is determined by the 

 influence of light. 



The sexual organs, antheridia and archegonia, are borne on special erect branches 

 of the thallus. The reproductive branches, which are contracted below into a 

 stalk, expand above into a profusely-branched upper portion. In this species, 

 which is dioecious, the antheridia and archegonia develop on different plants. 

 The branches producing the male organs terminate in lobed discs, which bear the 

 antheridia on their upper sides in flask-shaped depressions, each containing an 

 antheridium (Fig. 445 B}. The depressions, into each of which a narrow canal 

 leads, are separated from each other by tissue provided with air-chambers. (The 

 structure of the antheridia and spermatozoids is illustrated by Figs. 433, 434, 

 and the accompanying description.) The spermatozoids collect in a drop of water 

 on the disc, the margin of which serves to retain the water. 



The female branches terminate each in a nine-rayed disc (Fig. 446 A). The upper 

 surface of the disc, between the rays, becomes displaced downwards in the process of 



