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. ^ISd.—Marchavtia polymorpha. A, young thallus. B, an older thallns, with one 

 gerama^cup ; v, t), emargmare apical region of the two young branches of the thallns. 

 Ct a two-lobed thallns, nearing gemma-cups. I>, a portion of the upper surface of a 

 thallns (magnified), showing the lozenge-shaped areolse, each wii h a central stoma, sp. 

 I. to Vj., development of llie gemmae.. /., very young ; //., the terminal cell divided • 

 transvt rsely ; iff., a later stage, with divisions in various directions ; JV., F., 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 depressious 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 gemmse, 

 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 e^ch of these several hair-like papillae grow up, 



