78 A TEXT-BOOK OF BOTANY. 



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

 known as the PROTONEMA, or prothallus (Fig. 44). 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 differentiate 

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

 tutes the structure commonly regarded as the " moss plant " (Fig. 

 45, A). The leaf-bearing axis varies considerably in size; in 

 some cases it is but a millimeter high, whereas in some species, as 

 Polytrichum (Fig. 45), it may be several hundred millimeters in 

 height. At the tip of the branch the antheridium (Fig. 49, A) 

 and archegonium (Fig. 49, B) are formed. These organs are 

 developed in among the leaves and certain hairy processes, known 

 as paraphyses (Fig. 49, p) . They may both occur at the end of one 

 branch (Fig. 49, C) or they may occur on separate branches 

 (Fig. 49, D), when the plants are said to be monoecious, whereas 

 when these organs occur on separate plants (Fig. 49, A, B) the 

 plants are called dioecious. In the case of dioecious plants the 

 plant bearing the antheridium is frequently smaller and less com- 

 plex than the one producing the archegonium. As already stated, 

 the archegonium produces the egg-cell or female gamete (egg) 

 and the antheridium, the sperm cell or male gamete (sperm). 



The sperms in the Bryophytes are more or less filiform and 

 are provided with a pair of cilia at one end. The antheridia, 

 towing to the peculiar mucilaginous character of the cells, only 

 open when there is an abundance of moisture, when the sperms 

 are discharged and move about in the water, some being carried 

 to the archegonium, which likewise opens only in the presence of 

 moisture. With the transferral of the sperms to the archegonium 

 and the union of one of these with the egg which remains sta- 

 tionary, the work of the gametophyte may be said to be com- 

 pleted. The act of union of the egg and 'sperm is known as 

 FERTILIZATION, and when this is effected the next phase of the 

 life history begins. 



The egg after fertilization divides and re-divides within the 



