CHAPTEK XIX 

 THE THALLOPHYTES 



205. The thallophytes. The branch Thallophyta (meaning 

 thallus plants) contains the lowest forms in the plant kingdom. 

 A thallus is a simple vegetative body, without stems, leaves, or 

 roots, in the usual sense. The groups of the thallophytes fall 

 naturally into two series known as algae and fungi. 



"The algce. The algae contain chlorophyll or other pigments 

 which can do the work of photosynthesis. 



The fungi. The fungi have no chlorophyll, and must there- 

 fore obtain their food either as parasites from the tissues of 

 living plants or animals, called their hosts, or they may live as 

 saprophytes (meaning decay plants) upon the products of decay. 



The fungi are believed to have been derived from algae which 

 lost their color and gave up the processes of photosynthesis 

 because they happened to be placed under conditions favorable 

 to a life of saprophytism or parasitism. A perfect classification 

 of the thallophytes should show the relationships of the fungi 

 to the algae, but these are so little understood that it seems 

 best for the present to treat the two groups separately. 



The thallus is not really the distinguishing character of the 

 thallophytes, for some higher plants, as the liverworts, have 

 thalloid plant bodies, and some of the algae have a stem and leaf 

 structure as complex as that of the mosses. The thallophytes 

 are separated from the next higher group, the bryophytes (liver- 

 worts and mosses), by the absence of a peculiar type of life 

 history characterized by certain complicated reproductive organs. 

 These peculiarities cannot be understood until the liverworts 

 and mosses have been studied, so a full definition of the thallo- 

 phytes will be deferred until the end of Chapter xxiv. 



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