340 



PART IV. VEGETABLE TAXONOMY. 



are provided with elaters. The remains of the archegonium are 

 never borne on the top of the capsule. 



In habit of growth, nearly all of the species lie prostrate on 

 the substratum, presenting one side to the light and having the 

 other in shade. The two surfaces accordingly have a different 

 structure, rhizoids being usually developed in great numbers on 

 the shaded but not on the illuminated side ; the latter, in the 

 thalloid forms, also often possesses stomata, while the other does 

 not. The flattened forms usually branch dichotomously, and in 

 some of these there is no indication of leaves, while in others, 

 as in the Marchantias, scale-like bodies, doubtless to be regarded 

 as imperfectly developed leaves, occur on the under surface. 



In the foliose forms, there are two vertical rows of leaves, 

 very simple in their structure, on opposite sides of the stem, and 

 usually a third row of less perfectly developed ones on the side 

 next the substratum. 



There are four orders, as follows : 



(A) The Riccias are thalloid forms which branch dichot- 

 omously, and produce their antheridia and archegonia singly on 

 the upper side of the thallus. The capsule is globose, either 

 unstalked or short-stalked, does not bear elaters, and does not 

 spontaneously rupture when ripe. The plants are of small size, 

 and not numerous in species. Some of them, as Riccia fiuitans 

 and R. natans, are not uncommon c 



in fresh water ; others, as Riccia 

 glauca, grow on damp soil. 



(B) The Anthoceroteae pro- 

 duce a flattened, irregularly-lobed 

 thallus, which is closely attached 

 by means of rhizoids to the damp 

 soil in which they grow. They 

 produce erect, pod-like capsules 

 from archegonia imbedded in the 

 upper surface. These dehisce 

 lengthwise into two valves expos- 

 ing a columella. The elaters in 

 this group do not consist of coiled 

 threads or bands, as they do in the succeeding orders of this 

 class. The species are not numerous. Anthoceras laevis, one 



Fig. 549. — Anthoceras laevis. Por- 

 tion of thallus showing sporogonia, J, s, 

 dehiscing into two valves; c, columella. 



