110 



PLANT RELATIONS. 



72. Spore reproduction. — Besides vegetative multiplica- 

 tion most plants develop special reproductive bodies, 

 known as spores, and this kind of reproduction is known 

 as spore reproduction. These spores are very simple 

 bodies, but have the power of producing new individuals. 

 There are two great groups of spores, differing from each 

 other not at all in their powers, but in the method of their 

 production by the parent plant. One kind of spore is 



produced by dividing 

 certain organs of the 

 parent ; in the other 

 case two special bodies 

 of the parent blend 

 together to form the 

 spore. Although they 

 are both spores, for 

 convenience we may 

 call the first kind 

 spores (see Figs. 10G, 

 109), and the second 

 kind eggs (see Fig. 

 107).* The two special 

 bodies which blend to- 

 gether to form an egg 

 are called gametes (see 

 Figs. 107, 108, 109). These terms are necessary to any 

 discussion of the external relations. Most plants develop 

 both spores and eggs, but they are not always equally con- 

 spicuous. Among the algae, both spores and eggs are prom- 

 inent ; among certain fungi the same is true, but many 

 fungi are not known to produce eggs ; among moss-plants 

 the spores are prominent and abundant, but the egg is 

 concealed and not generally noticed. What has been said 



* It is recognized that this spore is really a fertilized egg, but in 

 the absence of any accurate simple word, the term egg is used for con- 

 venience. 



Fig. 107. Fragments of a common alga (Spi- 

 rogyra). Portions of two threads are shown, 

 which have been joined together by the grow- 

 ing of connecting tubes. In the upper thread 

 four cells are shown, three of which contain 

 eggs (z), while the cell marked g, and its mate 

 of the other thread each contain a gamete, 

 the lower one of which will pass through the 

 tube, blend with the upper one, and form 

 another egg. 



