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- 



Pig. 230. Jfarchantia polymarpha. A, young thnllns. B, an older thallus, with one 

 gemma-cup ; -e, v, emargmate apical region of the two young branches of the thallns. 

 C, a two-lobed thallus, oearing gemma-cap*. D, a portion of the upper surface of a 

 thallns (magnified), showing the lozenge-shaped areohe, each with a central stoma, up. 

 I. to VI., development of the genniur. /., very young ; //., the terminal ci-ll divided 

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

 later stages ; VI., outline of a fully developed gemma ; when it grows the new shoots 

 will start out right and left from the two depressions on its Bides. 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 email cup-shaped organs (4 to 6 mm. in diameter) de- 

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

 230). In each of these several hair-like papillae grow up, 



