CHAPTER XX 

 TYPES OF CRYPTOGAMS; THALLOPHYTES 



258. The Group Thallophytes. — Under this head are 

 classed all the multitude of cryptogams which have a 

 plant-body without true roots, stems, or leaves. Such a 

 plant-body is called a thallus. In its simplest form it con- 

 sists of a portion of protoplasm not enclosed in a cell-wall 

 and without much' of any physiological division of labor 

 among its parts (Fig. 125). Only a little less simple are 

 such enclosed cells as that of Pleurocoecus (Sect. 278) or 

 one of the segments of Oscillatoria (Sect. 268). The most 

 complex thallophytes, such as the higher algse and fungi, 

 have parts definitely set aside for absoi-ption of food and 

 for reproduction. The latter is sometimes accomplished 

 by more than one process and is occasionally aided by 

 some provision for scattering the reproductive bodies or 

 spores about when they are mature. 



259. Spores. — Before beginning the study of spore- 

 plants it is well for the student to know what a spore is. 

 A spore is a cell which hecomes free and capable of develop- 

 ing into a new plant. Spores are produced in one of two 

 ways : either asexually, from the protoplasm of some part 

 of the plant (often a specialized spore-producing portion), 

 or sexually, by the combination of two masses of proto^ 

 plasm, from two separate plants, or from different parts of 

 the same plant. 



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