SECT. I 



CRYPTOGAMS 



431 



grains, project from the lloor of the air chambers and perform the functions of 

 assimilating tissue. Chlorophyll grains are found also in the walls and roof of the 

 chambers, but only in small numbers. The intensity of tlie illumination exercises a 

 great influence on the formation of air chambers ; M'hen the illumination is very 

 weak they may not occur at all ("2). 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 jjarenchymatous 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. -371, l>). These contain a number of stalked gemmae, flat, biscuit- 

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



Fig. 370. — Marchantia polymorpha. A-C, 

 .successive stages in the formation of a 

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

 E, transverse section of a gemma ; .t, 

 point of attachment to stalk ; o, oil cells ; 

 r, colourless cells with gi-anular contents, 

 from which the rhizoids will develop. 

 (After Kny, .4-0x275; D.£x65.) 



Fig. 371. — ifarchc.ntia pohjmorpha. 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.) 



division of a single epidermal cell (Fig. 370) ; at maturity they become detached 

 from the stalk (at x, Fig. 370, D). They are provided with two growing points, 

 one at each of the marginal con.strictions, 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 gemmae Marchantia is enabled to multiply 

 vegetatively to an enormous extent. 



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

 of the thallus. The reproductive branches, wliich 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. 371, B). The depressions, into each of which a narrow canal 



