Chapter IX. 



Fungi. Kinds of Fungi* Sac Fungi. 



Sac fungi (Ascomycetcs). The second of the three great 

 groups of fungi is that of the sac fungi and this group is in 

 short easily distinguished because all of its members bear at 

 least some of their spores inside of sacs. These sacs may be 

 spherical or pear-shaped or long-cylindrical, according to the 

 plant, and they always contain a definite number of spores. 

 The sacs in the simplest of these fungi are borne irregularly 

 upon the loose weft of the mycelium but in the very great ma- 

 jority of sac-fungi they are borne in capsules of various shapes 

 and often of great complexity. 



Sometimes these capsules are little, black spheres, as in the 

 powdery mildews, with or without an opening, while in others 

 they may be borne in the fruiting bodies known as truffles or in 

 the cups of cup-fungi. According to our present knowledge a 

 breeding act seems to precede the formation of the sacs and in 

 some cases one, in others, numerous, sacs may arise as the re- 

 sult of a single breeding. A vast number of sac fungi form 

 more than one kind of spore in fact many produce two 

 or three so-called accessory spores, so that the study of 

 such forms becomes a very difficult matter. Indeed, one may 

 find many of these accessory forms without the main sac-form 

 and it is then often exceedingly difficult or altogether impossi- 

 ble to even determine the fungus. Thousands of such fungi 

 have been found many causing important diseases of plants 

 which are thus imperfectly known and are described un- 

 der provisional names until more facts are discovered about 

 their life-stories and their proper sac forms. Not until then can 

 they be accurately and permanently classified. Such fungi are 

 called imperfect fungi. It is even probable that many have for- 

 gotten how to form their sacs and now produce only the acces- 

 sory spore-forms and thus present an actually imperfect life- 



