THE SPORE-BASE FUNfil 501 



formed at the tips of vertical liyphiE by the separation of 

 individual cells as shown at c. Each of the dust-spores thus 

 formed is regarded as representing a degenerate spore-case 

 containing but a single spore. Minute sac-like cases contain- 

 ing eight sac-spores are formed within a spherical envelope 

 from the feeding hyjihte. 



What appear to be male and female gametangia arise where two 

 hyphae cross (Fig. .329, a, b, c), the female coming from the lower 

 hypha, the male from the upper. Fertilization has not l:)een ob- 

 served and all sexuality seems to have been lost in these plants; 

 but from what we have called the female cell there are develo])efl 

 several eight-spored sacs or o-sc/,' as they are called, while from the 

 supposed male grow up a number of enveloping branches consisting 

 of many short cells so crowded and joined as to make a complete 

 protective envelope. 



Fungi related to the mildews and sometimes parasitic 

 upon them, as shown in Fig. 328, b, d, produce very minute 

 dust-spores which are crow^ded within a case resemljling 

 the envelope just described. When the sac-spores are set 

 free under favorable conditions they germinate like the dust- 

 spores. 



Comparing Erysibe with Coleochsete we find some significant 

 resemblances which make it comparati-\'ely easy to sui)pose that 

 fungi of this sort have descended from such algce; — the multicellular 

 creeping branches of the thallus becoming multicellular creeping 

 hypha>; the sporangia, dust-spores; the female gamctangium de- 

 veloping into a group of asci, while a neighboring cell, simulating 

 the male gametangium, gives rise to an enveloping rind. These 

 changes are such as might be expected in passing from the ariuatic 

 and sun-using mode of life to the aerial and parasitic. Ascospores 

 characterize the Class Ascomycetes. 



183. The spore-base fungi (Class Basidiomycetes) are 



well represented by the mushrooms, although very many 

 widely diverse forms are included among its other members. 

 The common field mushroom (Figs. 119, 330) vegetates by 

 subterranean hyphte feechng upon decaying organic matter 

 in the soil. From this mycelium arise, finally, compact masses 

 of hyphae forming fruit-boches which soon become differ- 

 entiated into a vertical stalk and a horizontally expanded 

 1 As'cus < Gr. askos, bag. 



