MARCHANTIA POLYMORPHA 125 



into an air-cliamber; to the naked eye the pores look 

 like mere dots. The air-chambers are relatively large; 

 they are, as it were, roofed, and air finds access only 

 through the pores or stomata. Filaments of nearly 

 globular cells rise from the floor of each chamber; these 

 cells contain chlorophyll, and are the principal means 

 of carbon-assimilation. The whole upper surface is of 

 a dull, dark green colour. 



Plate IV., Pigs. 1, b, and 2, show what are called 

 " gemmae cups," which are usually found growing over 

 the midribs; the cups have toothed edges, and each 

 contains a number of flattened, stalked gemmae (L. 

 gemma, a bud); a single gemma, enlarged, is shown in 

 Fig. 3 of the same plate. When the gemmae are mature, 

 they become detached and scattered, and if they drift 

 to a suitable site, they grow into new plants; they are 

 an asexual means of propagation. 



The reproductive organs occur on highly specialized 

 branches of the thallus, and the sexes are represented 

 on different plants ; they do not appear together on the 

 same plant. These specialized branches are erect, 

 narrowed into a stalk below, and expanded into an 

 umbrella-like, lobed disc at the apex. A branch bearing 

 male organs, antheridia, is called an " antheridiophore" 

 (Plate IV., Fig. 1, a), and the antheridia are found on 

 the upper surface of the lobes of the disc, in flask-shaped 

 depressions (see same plate, longitudinal section of 

 antheridiophore. Fig. 4, e ; and Fig. 5, single antheri- 

 dium, enlarged). The antheridia produce biciliated 

 male elements, the spermatozoids (Fig. 5, g). 



The specialized branches borne by the female plants 

 are called " archegoniophores," because they bear 



