Ch. VI, 6] 



ASEXUAL REPRODUCTION 



299 



)) 



The only plants which reproduce exclusively by asexual 

 methods, so far as known, are the very simplest Algae and 

 the Bacteria. Their single-celled bodies divide across into 

 two ; the halves grow to full size and fall apart (Fig. 210) ; 

 and thus we have asexual reproduction by division. One 

 might think also that the higher Fungi should be included 

 in the asexual category; but newer studies seem to be 

 showing that these plants possess a form of fertilization. 



In addition to division, the asexual methods include 

 specialized vegetative bodies, potential vegetative parts, and 

 asexual spores. 



1. Specialized vegetative bodies. These are mostly of the 

 nature of separable buds, formed on thallus or shoot and 

 later set free, when they 

 grow directly to new 

 plants. Such bodies are 

 found in Algae and Fungi, 

 especially the Lichens, 

 and reach fuller devel- 

 opment in the higher 

 groups. Thus, some 

 Liverworts produce in 

 special cups on the thallus 



many symmetrical flat bodies called gemmae (Fig. 211), which, 

 washed out or blown to some distance, produce there new 

 plants. Some Ferns produce on the margins of their fronds (fj 

 little buds , which sprout and continue their growth when \ f 

 the leaves are dropped. Identically the same feature is ^-^ 

 found in the Life-plant, or Bryophyllum (Fig. 43), which 

 has buds on the margins of its leaves, and thus can produce 

 new plants when the leaves fall on the ground. Essentially 

 the same principle is involved in the formation of little 

 plants at the ends of the runners in the Strawberry, as earlier 

 described (page 189). Some waterweeds form compact win- 

 ter buds, which separate and float away to start new plants 

 in the spring. The larger Lilies produce in the axils of their 



Fig. 210. — Asexual reproduction, by 

 division, of Pleurococcus, a green Alga 

 which grows upon tree trunks; much 

 magnified. 



The smaller cells thus formed soon grow 

 to full size. 



