CHAPTER IV. 



REPRODUCTION OF PLANTS. 



Vegetative or asexual method. — Sexual method. — Gradual evo- 

 lution and advantages of the latter method. — Alternation of genera- 

 tions. — Cross-fertilization. — Protection of reproductive portions of 

 plants. 



IN many of the priiEfltive types of plant life the 

 only known mode of reproduction is by fission 

 or cell division, as already explained in the case of 

 Pleurococcus vulgaris. In other simple multicellular 

 fresh-water Algss, as the species of Nostoe, that form 

 blue-green or brownish gelatinous masses on damp paths 

 and shady places after wet weather, the cells are arranged 

 in a single row, forming long filaments that are variously 

 contorted and imbedded in mucilage ; during the repro- 

 ductive phase these filaments break up into short pieces 

 which escape from the gelatinous matrix, each fragment 

 forming the starting-point of a new individual, the fila- 

 ment rapidly increasing in length by repeated fission of 

 its component cells. In vegetative or asexual repro- 

 duction the portion destined to form the starting-point 

 of a new individual always consists of one or more cells 

 formed by the ordinary method of cell-division, whereas 

 in the sexual mode the reproductive body is invariably 

 the result of the blending together of the protoplasm 



