4 THE LOWER FUNGI— PHYCOMYCETES 



Although the bacteria lack the blue-green color their resemblance 

 to the Cyanophyceae in other respects is certainly striking. 



Bacteria. — The absence of chlorophyll in the bacteria has 

 influenced most students to place these forms near the fungi. 

 In some earlier classifications the two groups were merged. 

 Even de Bary (1887) treated them side by side. It is true that, 

 lacking chlorophyll, they have a type of physiology similar to 

 that of the fungi, but differences in morphology are marked and 

 indicate clearly that the two groups are at best only remotely 

 related. Among the lower fungi there seem to be no forms 

 through which a connection with the bacteria may be logically 

 indicated. In the fungi the nucleus is highly organized and 

 evident, the cell wall is of a different composition from that of 

 the bacteria, and organs of locomotion are wholly dissimilar. 



Although the bacteria constitute a very large and extremely 

 important group of colorless lower forms, it is neither possible 

 nor appropriate to incorporate in a book on lower fungi any 

 detailed statement concerning them. Instead, the student is 

 referred to the many reference works which have appeared in the 

 broad field of bacteriology. 



Lichens. — In the above outline of the major subdivisions of 

 the Thallophyta the lichens (Lichenes) are listed as a separate class 

 coordinate in rank with the fungi. This disposition of the group 

 is made chiefly with the idea of isolating these forms for the 

 purpose of discussion. The actual position of the group in a 

 phylogenetic arrangement is somewhat uncertain and debatable. 

 The thallus of the lichens is clearly fungous in character, and 

 the fruiting structures are essentially identical with those of the 

 true fungi. In fact, the lichens differ from the fungi only 

 in one important respect. Their thallus, in a very early stage 

 of development, incorporates within itself algae encountered on 

 the substratum, and these exist throughout its life in the inter- 

 stices between its hyphae. The two organisms, thus brought 

 together, considered as a unit, constitute a Hchen. They main- 

 tain an intimate food relationship, which has been assumed by 

 many workers to be mutually advantageous, and has long been 

 called symbiosis. Experiments have demonstrated that the 

 algal constituent of this dual combination is capable of existing 

 free in nature, and indeed has its own proper place in the classi- 

 fication of the algae. In any given genus of lichens the alga is 

 usually a single definite species. In the group as a whole many 



