Ch. VI, 61 



ASEXUAL REPRODUCTION 



301 



3. Asexual spores. A spore is typically a single-celled 

 body which can grow directly into a new plant. Many of 

 the simpler Algte throw out into the water tiny spores which 

 swim freely about by aid of small cilia, and hence are called 

 ZOOSPORES (Fig. 213) ; they resemble closely the gametes 

 later described (page 303), but grow without any fusion 

 into new plants. Higher Alga; also produce such spores, 

 which are thrown off to 

 drift with the currents, 

 as will be described in 

 Part II of this book. 

 Most of the Fungi pro- 

 duce asexual wind-scat- 

 tered spores, usually in 

 very great number, and 

 minute as the dust, 

 either on the gills, as 

 with Mushrooms, or in 

 special long-stalked 

 spore cases, as in Molds 

 (Fig. 214), or in other 

 equivalent ways. 

 Liverworts and Mosses 

 produce spores in their 

 capsules, and Ferns in 

 the "fruit dots" on the 

 under sides of their 

 fronds, as will later 

 more fully appear. In all of these groups except the Fungi, 

 and even obscurely in them, occurs also a sexual reproduc- 

 tion with fertilization, as already described, while moreover 

 there exists usually, and perhaps alwa^^s, a marked alter- 

 nation between the sexual and asexual methods. This 

 latter subject merges into the so-called alternation of 

 GENERATIONS, a matter of very great morphological inter- 

 est, to which we shall return in Part II. 



Fig. 21.3. — Zoospores, asexual unicel- 

 lular reproductive bodies, of Algae ; highly 

 magnified. 



The forms are typical. All swim by action 

 of the hair-like cilia, — towards the cilia. 



