214 PHYLUM VII. CARPOMYCETEAE 



THE DISK "LICHENS" (ORDER DISCOLICHENES) 



337. The primitive ASCIIS Fungi (Ascosporeae) appear to 

 have been parasitic on small, green algae (MYXOPHYCEAE 

 and KHLOROPHYCEAE), and indeed this may have first 

 taken place in the water. It is known that some of the 

 proper Red Algae are parasitic, and the view here taken is 

 that in the Disk Lichens we have a group of plants in which 

 the parasitism has gone further, and has resulted in so 

 great a modification of the plant body as to place them in 

 another phylum. 



338. The Disk Lichens abound almost everywhere 

 on tree-trunks, rocks, old roofs, and in many regions upon 

 the ground. They are for the most part of a greenish- 

 gray color, and hence are often called "Gray Mosses." 

 Other colors, as black, purple, yellow, and white, are also 

 common. 



339. The plant-body of a Disk Lichen is composed of 

 jointed, branching, colorless filaments, similar to those in 



the other fungi, but usually more or less 

 compacted together into a thallus, or even 

 a branching stem. They obtain their 

 nourishment from little green Myxophy- 

 FIO. 95. Section ceae or C hlorophycese to which the fila- 



of a Disk Lichen. , .,. 



ments attach themselves parasitically. 

 These little hosts, which at first live free in water or on 

 moist surfaces, eventually come to live in the midst 

 of the moist tissues of the fungus parasite. They 

 were formerly supposed to be parts of the lichen itself, 

 and were called "gonidia," an objectionable term which 

 is still in common use. 



340. Disk Lichens are all of rather small size, vary- 

 ing from a millimeter or so, to 20 or 30 centimeters in 

 length. For the greater part the plant-body is flattish, 

 and adherent to the surface upon which it grows, but 



