190 OUTLINES OF PLANT LIFE. 



different stages or in different parts spores which are unlike 

 in form and nature (compare / and si, fig. 141)- In almost 

 all cases there is a supply of reserve food within the spore, 

 which varies in amount with the conditions under which they 

 are formed. It is ordinarily greater in resting spores than in 

 those intended for immediate growth. 



267. Growth. — Spores germinate by absorbing water, 

 thus bursting the more rigid outer layer or layers of the cell- 

 wall. The inner layer then grows in area to accommodate 

 the increasing protoplasm, which so controls the mode of 

 growth as to produce a plant of definite form. In many 

 cases the plant produced is essentially like that which gave 

 rise to the spore. In others it is different, but sooner or 

 later in the life cycle the same form recurs. 



268. Origin. — Non-motile spores are either free, being 

 produced at the ends of branches specialized for that pur- 

 pose, or enclosed in a spore case. Often the same plant 

 forms spores by both methods at different stages in its 

 development. 



269. Free spores. — The formation of free spores is con- 

 fined to the lower plants, and is especially characteristic of 

 the non-aquatic fungi. The branches producing spores may 

 occur singly, or, more commonly, they are grouped at 

 certain points, forming a spore-bed (fig. 141). If the fungus 

 develops its mycelium in the interior of a host, the formation 

 of a spore-bed is often necessary to rupture the host, so that 

 the spores may be brought to the surface and set free. Thus 

 the spore-beds of parasitic fungi commonly blister the surface 

 of the host by lifting up its outer tissues {eo, fig. 141). 



Spores may be produced either singly at the ends of the 

 branches, or in chains (fig. 142). 



A modification of the production of spores singly occurs 

 when the branch destined to produce them gives rise to two 

 to eight very slender branches, each of which enlarges at the 



