344 



BOTANY. 



447. — The leaves, when present, are usually in two rows 

 (distichous), and are either opposite or alternate ; they are 

 entire, serrate, or even lobed. There is frequently a third 

 row of leaves (called amphigastria) on the under side of the 

 stem. 



448. — Most Liverworts are small in size, ranging from a 

 few millimetres to several centimetres in length. They 

 grow for the most part in moist places, upon the ground, or 

 upon rocks, or the bark of trees. All are chlorophyll-bear- 



Fig. 230. — Marchantia polymorpha. A, young th«llu8. B, an older thallns, with one 

 gemma-cup ; v, v, emarginate apical region of the two young branches of the thallus. 

 C, a two-lobed thallus, rearing gemma-cups, i?, a portion of the upper surface of a 

 thallus (magnified), showing the lozenge-shaped areolse, each with a central stoma, sp. 

 I. to VI. ^ development of the gemmae. /., very young ; J/., the terminal CfU divided 

 transversely; III., a later stage, with divisions in various directions ; IV., V., still 

 later sta^jes ; VL, outline of a fully developed gemma ; when it grows the new shoots 

 will start out right andleft from the two depressions on its sides.— After Sachs. 



ing plants, and they are usually of a green or brownish 

 green color. 



449. — The asexual reproduction of Liverworts takes 

 place by means of bodies of a peculiar kind, called gemmae, 

 which are usually produced in special organs. This mode of 

 reproduction is well illustrated in the genus Marchantia, in 

 which small cup-shaped organs (4 to 6 mm. in diameter) de- 

 velop upon the upper side of the thallus {B and C, Fig. 

 330). In each of these several hair-like papilla grow up, 



