696 TEE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



Phylum 3.— ARCHEGONIAT^. 



Plants showinff a well-marked altei-nation of generations, that is of a sexual 

 (oophyte) and an asexual generation (sporophyte). The latter reproduces the 

 former by means of spores, the former the latter by means of egg-cells contained in 

 archegonia. Fertilization is by means of spermatozoids which swim in water. 



t 



Class I.— BRYOPHYTA . 



The sexual generation is in the greater number of cases a leafy shoot, arising 

 from a branched, filamentous protonema. The asexual generation, which arises 

 from the archegonium, is a stalked or sessile capsule containing spores; it is 

 destitute of leaves, and never becomes independent of the oophyte. 



Alliance XX. — Hepaticae, Liverworts. 



Oophyte nearly always dorsi- ventral; either thalloid or leafy. Protonema incon- 

 spicuous. Spoi-ophyte a stalked or sessile capsule containing spores and usually 

 elaters. A calyptra is not present. 



Families: Ricciacece, Marchanfiacece, Anthocerotacece, Jungermanniaeece. 



The oophyte generation in the first three families is a branched, ribljon-like, or 

 lobed thallus (cf. fig. 196 \ p. 2.3), showing a distinction between its upper and lower 

 surfaces, i.e. is dorsi-ventral. In the Jungermanniacese it is likewise thalloid in some 

 forms, but in the great majority the oophyte has the form of a leafy shoot. The 

 oophyte communicates with the substratum by means of rhizoids. The complete 

 oophyte is preceded by an inconspicuous filamentous growth, the protonema, which 

 arises directly from the spore, but tliis stage is not so well marked as in the Mosse.s. 

 The sexual organs are borne usually in groups either in little depressions or upon 

 special outgrowths of the thallus, or, in the leafy forms, are collected together into 

 little "flowers" at the tips of the shoots or in the axils of the leaves. The female 

 organs or archegonia are flask-shaped bodies with long necks, as in mosses. The 

 egg-cell is contained in the enlarged basal portion, and on fertilization develops into 

 the sporophyte or spore-capsule. The antheridia are delicate, stalked, oval or club- 

 shaped bodies in which the 2-ciliate spermatozoids are developed. They resemble 

 those of Chara, shown in tig. 37-1' (p. 660). The spore-capsule develops within the 

 archegonium ; its lower portion (in all but the simplest cases) forming a " foot " or 

 sucker which remains imbedded in the substance of the oophyte, its upper portion 

 forming the capsule proper. In many forms, particularlj' in the Jungermanniacese, 

 a stalk is developed between foot and capsule, so that the latter is ultimatel3' hoisted 

 up. The capsule does not burst through the archegonial wall until the spores are 

 ripe, nor is a portion of the archegonium raised up as a cap on the capsule as 

 happens in the Mosses. The capsule ultimately opens by splitting into valves. In 

 nearly all cases elaters are present with the spores. They are long thread-like ceUs 

 with spiral thickening of tlie wall, and as they dr^' become very hygroscopic and 



