THE CREAT GRfiUPS OF BEYoFHYTES 



309 



203. Marchantia forms. — In tliin line the simple tliallus 

 griidually Ix'comes (diang-od into a very eonijilex one. Tlie 

 tliallus retains its simple 

 outlines, but becomes thick 

 and differentiated in tissties 

 (groups of similar cells). 

 The line may be distin- 

 guished, therefore, as one 

 in which the dift'erentia.- 

 tion of the tissues of the 

 gametojihyte is ennihasizod 

 (Figs. 280-282). Jn Mar- 

 iliiniiia proper the tliallus 

 becomes very complex, and 

 it may he taken as an illus- 

 tration. 



The tliallus is so thick 

 that tliere are very distinct 

 green dorsal and colorless 



ventral regions (Fig. 283)). The latter jiuts out numerous 

 rhizoids and scales from the single layer of epjidernial cells. 

 Above the ventral epidermis are several layers of colorless 



^k 



Fn;. 3sn \ ■\(i\ small spc f ks (if Ti}<< xt 

 oiic nt till iM Lii li iiiti i forms 1 a 

 ^roiip ot 111 illiis ])ndi(s Kli_'htl\ tn 

 lar^( (1 / s, , (i,„i of I tliiJIiis slu w 

 iim I 111/ kN 111 I t\\ ) I _iiiii I nil 

 l)i.'(lil( d aul (DiinnmiK iliii^ with the 

 ontsuk lj> tnliiil ii p i*-s it^cs iii tlip 



tliallLlf^. — Att( 1 S I lLASLLIv(,b,K. 



Fia. 'i'^\. li'irnonirpiifi^ a Marcliantia form, showing numerous vliizoids from \eii(ral 

 i^iirlace, (Ik- dicliolomous branchin.i,', and the position of the sporogonia on Iht; 

 dorsal surface along the " midribs. "—(-Joldiiergku. 



