CHAPTER VII 



THE MICROSCOPIC PLANTS— PROTOPHYTA* 



THE group of intermediate flagellates is distributed by bota- 

 nists among a number of classes. The term protophyta, 

 indicating the same position among plants that the term pro- 

 tozoa does among animals, is rarely used except in a descriptive 

 sense, and then it is interchangeable with the term algae. The 

 organisms included among the algae are by no means limited to 

 the unicellular forms; hence it is impossible in a work on "The 

 Smallest Living Things" to treat all of them. It would be more 

 simple to consider them, as zoologists do, as groups of unicellular 

 organisms without regard to their possible relationships to higher 

 types, than to treat them, as botanists do, as ancestral types of 

 higher forms of plants. The green flagellates in particular are 

 regarded by most botanists as the forerunners of filamentous 

 algae and of thallophytes't' generally. A captious critic might 

 well question the advisability of assuming that any present day 

 free-living forms are actually ancestral to any present day higher 

 types. With equal authority such forms might be regarded as 

 retrogressive types derived from higher forms of the past, a 

 view that is indeed held by many. 



Whichever view we take as to the phylogeny (race history) 

 of these minute forms of life it is expedient to arrange them in 

 some sort of sequence and, as far as possible, in an ascending 

 order of complexity. In transferring the chlorophyll-bearing 

 flagellates to the botanists we abandon a relatively simple classi- 

 fication for one that is far more involved. 



In botany the lowest form of the green or chlorophyll-bear- 

 ing plants is known as the thallophyta, a group distinguished from 

 most of the higher plants by the possession of relatively uncom- 

 plicated body structures and by simple reproductive processes. 



* See "The Plant World, pages 13-25, of this Series. 



t The thallophytes include the algae, the fungi, and the lichens. 



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