46 



BOTANY AND PHARMACOGNOSY. 



body or thallus lies more or less close to the substratum or rises 

 somewhat obliquely, whereas in the Mosses the part we designate 

 as the plant is in all cases an upright leafy branch. The moss 

 plant is said to have a radial structure from the fact that the 

 leaves radiate from a central axis, while in the Liverworts the 

 thallus is dorsiventral, that is, as a result of its habits of growth, 

 it is characterized by having a distinct upper and lower surface. 

 The Life History of this group of plants may probably be 

 best illustrated by following that of a moss plant. Beginning 

 with the germination of an asexual spore which is microscopic in 



Fig. 27. A common moss (Funaria). A, germinating spores: v, vacuole; w, root- 

 hair; s, exospore. B, protonema about three weeks after germination: h, procumbent 

 primary shoot; b, ascending branch of limited growth; K, bud or rudiment of a leaf-bearing 

 axis with root-hair (w). — After Sachs. 



size and which germinates on damp earth, there is produced an 

 alga-like body consisting of branching septate filaments, which is 

 known as the protonema, or prothallus (Fig. 27). The Proto- 

 nema lies close to the surface of the ground and is more or less 

 inconspicuous except for the green color. From the lower por- 

 tion thread-like processes, or rhizoids consisting of a row of cells, 

 are developed, which penetrate the ground. Sooner or later lateral 

 buds arise from some of the lower cells. Growth continues from 

 an apical cell which divides and gives rise to cells that dififerentiate 

 into stem and leaves, forming an upright branch, which consti- 

 tutes the structure commonly regarded as the " moss-plant " 



