110 CLASSIFICATION OF PLANTS 



257. Order i. The Peris poreacea comprise the mildews and the blue 

 molds. In this group the asci are completely enclosed in a minute spher- 

 ical fruiting body, the perithecium. The mildews are parasitic on the 

 leaves of higher plants as exemplified by the common grape and lilac mil- 

 dews. The blue molds are saprophytic on decaying fruits, preserves, 

 bread, leather, etc., and are usually readily distinguished from the black 

 molds (Phycomycetes) by the color and by the conidia. 



258. Order 2. In the Discomycetes the asci are borne in concave disk- 

 shaped fruiting surfaces (apothecia). The species of this order are very 

 common and are usually saprophytic. They are most frequently found 

 on decaying wood. The edible morel (Morchella) belongs to this order. 



259. Order 3. In the Pyrenomycetes the perithecium is flask shaped 

 with a pore through which the spores escape. In the mature condition 

 the fruiting bodies are usually black. The Pyrenomycetes are in part 

 parasitic; some on other plants as the black knot of plumb trees or the 

 ergot of rye and some in the bodies of insect larvae. Many forms are 

 saprophytic on bark, decaying wood, etc. 



260. Order 4. The Tuber acea are saprophytic underground in forest 

 humus. The perithecia are large spherical bodies without opening. 

 Some forms are edible. 



261. Order 5. The Exoasci are parasitic on trees and stimulate the 

 tissues of the host to abnormal growth thus forming in certain cases 

 "witches' brooms." 



262. Order 6. The Saccharomycetes (yeasts) are microscopic unicellular, 

 saprophytic fungi. They are important as the chief agents in the various 

 fermentation processes connected with the making of bread, wine, beer 

 and other alcoholic liquors. Reproduction takes place by budding 

 (conidia) and under favorable conditions spores are formed endogenously 

 within a cell (ascus). 



263. Lichens. The lichens are one of the most common and most widely 

 distributed types of vegetation. They may be found on almost any kind 

 of stable surface, on rocks, tree trunks, or on the surface of the earth. 

 They are often confused with mosses but are readily distinguishable. 

 The color is usually gray or brown but never chlorophyl green. The 

 fruiting surfaces are frequently brilliantly colored. The form of the plant 

 is thalloid, never differentiated into true stem and leaf. Serious objection 

 may be made to ranking them as a class because a lichen is in reality only 

 a symbiotic combination of an alga and a fungus, either of which may be 

 grown independently of the other. The algae concerned would by them- 

 selves be classed as Cyanophyceae or as Chlorophyceae of the simpler forms. 



