CHAPTER IV. — REPRODUCTION. 257 



Reproduction. All plants possess the power of giving rise 

 to new individuals, and this may take place in either one of two 

 general ways, (i) by some form of cell division, and (2) by the 

 union of two cells, at first distinct. The former mode is called 

 asexual, and the latter, sexual reproduction. In the asexual mode 

 we may distinguish between vegetative reproduction, in which 

 the parent plant throws off or separates from itself ordinary vege- 

 tative cells, and spore-reproduction, which consists of the sepa- 

 ration of specialized cells called spores. The vegetative mode 

 is represented in a very simple way by many of the low forms of 

 plant life. The Red Snow-plant of the Arctic regions and the 

 Bacteria multiply with astonishing rapidity by the simple process 

 of fission. Except that the cells become independent of each 

 other, instead of remaining together to form colonies, the process 

 resembles the cell-multiplication which takes place in the higher 

 plants during growth. In the yeast and its allies, new individ- 

 uals are formed by budding or by internal cell-formation. Most 

 plants, even those belonging to the higher orders, have the 

 power to multiply vegetatively. The Common Liverwort (Mar- 

 chantia), for example, produces on the surface of its fronds little 

 cup-like organs from which rounded masses of green cells are 

 set free to give origin to new individuals ; the Tiger Lily repro- 

 duces by means of bulblets formed in the leaf-axils ; and many 

 plants, multiply, as we have seen, by bulbs, tubers, stolons, 

 offsets, etc. 



Spore-reproduction by the asexual process is exemplified in 

 many flowerless plants. The spores which are produced in such 

 enormous numbers on the gills of the common Mushroom, many 

 of the motile spores so commonly produced by the fresh-water 

 Algae, and the ordinary spores of Equisetums, Club-Mosses and 

 Ferns, are all products of this process. The spores are commonly 

 borne in a special organ, called a sporangium. 



There are also two principal modes of sexual reproduction. 

 The simplest is by conjugation, which, as already explained, 

 means the union of two cells that, to all appearance, are pre- 

 cisely alike. There are two varieties of this mode, one in which 

 the union takes place between ordinary vegetative cells, as in 

 Spirogyra, Fig. 397, and the other in which the union is between 

 zoospores as in Pandorina, Fig. 484, o and c. The product, in 

 either case, is callen a zygospore. 



