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A TEXTBOOK OF BOTANY 



[Ch. XI 



even live submerged. They represent without doubt the 

 transitional group between water plants and land plants, 

 though the gap is wide between them and any known Algae. 

 Some 4000 species are known, divided into four orders. 



Order 1 . Ricciales : the Riccias and kin. 

 Order 2. M arch anti ales : the Marchantias and kin. 

 Order 3. Jungermanniales: the Leafy Liverworts. 

 Order 4- Anthocerotales : the Anthoceros and kin. ' 



Order 1. Ricciales: the Riccias and kin. These have 

 a true thallus, suggestive of Algae, but possessing intercel- 

 lular spaces like the 

 higher plants. They 

 grow upon wet ground, 

 but some forms are 

 floating and can live 

 submerged according to 

 circumstances (Fig. 

 339). The archegonia 

 and antheridia are 

 sunken in a groove along the middle line of the upper 

 surface, and the fertilized egg cell grows into a simple, 

 spherical, unstalked sporogonium, containing many spores. 



Order 2. March anti ales: the Marchantias and kin. 

 These include the best-known Liverworts, of which the very 

 common Marchantia polymorpha, abundant in the woods 

 of north temperate regions, and therefore much studied in 

 botanical laboratories, may be taken as representative 

 (Fig. 340). The lobed and somewhat liver-shaped thallus 

 was formerly supposed, in accord with the " doctrine of sig- 

 natures," to have this form as an indication of sovereign 

 virtues in the cure of diseases of the liver, — whence its 

 class name. It creeps on the ground, to which it is at- 

 tached by absorbing rhizoids. Its tissue is chiefly a color- 

 less storage parenchyma overlaid by rhombic air chambers, 

 which open through the epidermis by chimney-form, non- 



Fig. 339. — Riccia fluitans, natural size. 

 Left, submerged form ; right, land form. 

 (After Goebel, from Strasburger.) 



