212 PLANT LIFE. 



to loosen pieces of definite length, which creep out of the 

 jelly, grow, and thus produce new colonies. 



The greater size reached by most multicellular plants soon 

 renders impossible the continuance of this method of repro- 

 duction, except among those whose cells arc all alike. Should 

 such separation into nearly equal parts occur among more 

 highly specialized plants, it is evident that one portion might 

 easily be left without nutritive organs adapted to its needs. 

 The higher plants, therefore, specialize certain regions or 

 members, where, by division or budding or similar processes, 

 reproductive bodies may be formed. 



II. Spores. 



304. Sexual and non-sexual spores. — A spore is a single- 

 celled body capable of producing a new plant. Spores may 

 be formed either by a process of growth or by a sexual act — 

 i.e., the union of two cells. The former are called non- 

 sexual spores ; the latter, sexual spores. Only non-sexual 

 spores are discussed in this chapter. 



305. Structure. — While a spore is generally composed of 

 one cell, the term is extended to include two- to many-celled 

 bodies which are formed in the same way as the simpler 

 ones. In fact, no clear distinction in form or structure can 

 be drawn between spores and brood-buds. (See 1" 361.) 



306. Motile spores. — Spores may be either naked and 

 motile or furnished with a cell-membrane and non-motile. 

 The former are commonly produced by plants which pass all 

 or part of their lives in water, such as the algre and aquatic 

 fungi. They are usually pear-shaped and furnished with one 

 or more cilia, by means of which they swim about (fig. 168). 

 When locomotion was supposed to be a distinctive power of 

 animal bodies they were called zoospores, a name still re- 

 tained. They are also called swarm-spores. 



