CHAPTER XXIII 

 CHARACTERISTICS OF SPORE-PLANTS 



262. Definition of a Spore-Plant A spore-plant is one 



which does not form seeds but is reproduced by means of 

 a one-celled reproductive body called a spore?- Such bodies 

 do not contain an embryo ; they are of microscopic size and 

 in all ways are far simpler than seeds. 



263. Diversity among Spore-Plants. — Spore-plants are 

 extremely diverse in their size, structure, and life habits, 

 and in the details of their reproductive processes. 



The simplest and smallest among them are one-celled 

 organisms, not more than a fifty-thousandth of an inch in 

 diameter, while the largest seaweeds are nearly or quite a 

 thousand feet in length, and tree ferns reach a height of 

 thirty or forty feet, with ample spreading crowns (Plate XI). 



The pale or colorless spore-plants, such as bacteria, 

 molds, and toadstools or mushrooms (Figs. 169, 172, 185), 

 can live onlj- as parasites, taking their food from living 

 animals or plants, or as saprophytes, feeding on the prod- 

 ucts of decay. 



The green spore-plants, however, carry on their nutritive 

 processes as the higher plants do (Cliapter xin), and in 

 all such relatively complex forms as the horsetails and 



1 Seed-plants (commonly called floTvering plants) also produce spores (Sect. 

 383), but those forms which are treated in Chapters XXIII-XXVII may fairly 

 be called spore-plants since the spore is their highest means of reproduction. 



2U 



