CHAPTER XIV 

 THE THALLOPHYTA 



The most simple and primitive of the four divisions of the 

 plant kingdom are the ThallopJnjta or thallophytes. This is 

 a huge assemblage of species, about 80,000 in all, which dis- 

 play a wide varietj^ in their structure and life histories. The 

 name " thallus-plants " refers to the character of their vegeta- 

 tive body, which is typically a thallus, or mass of tissue with little 

 differentiation into such diverse organs as we find among the 

 higher plants. It is usually rather small, and is often minute. 

 This simplicity of their vegetative structures, together with 

 their generally simple and primitive methods of reproduction, 

 are the chief features which distinguish the thallophytes as 

 a whole. 



To construct a truly natural classification for such a hetero- 

 geneous group is a very difficult task indeed. The division as a 

 whole is usually separated into two main series: The Algae, which 

 possess chlorophyll or a similar substance and may thus live 

 independently, and which include all the seaweeds, together with 

 the pond scums and similar plants of fresh water; and the Fungi, 

 which lack chlorophyll and can therefore exist only as saprophytes 

 or parasites, and to which belong the multitude of bacteria, molds, 

 mildews, blights, rusts, toadstools, and mushrooms. The fungi 

 have evidently arisen from several different groups of algae, so 

 that the two series parallel one another somewhat in their various 

 characteristics. It is more convenient to treat each separately'' 

 however, incidentally pointing out such relationships as seem 

 clear between various groups in the two series. 



THE ALGAE 



The algae are commonly divided into four classes, the Blue- 

 green Algae, the Green Algae, the Brown Algae, and the Red 

 Algae. The differences in color which have given rise to these 

 names are incidental and are accompanied by more deeply 

 seated distinctions. 



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