FUNGI. 15 



or almost closed, hardened receptacles, but are not themselves 

 enclosed in sacs or asci. There are therefore, four different 

 stages in the life history of such a fungus, each characterized by 

 a special form of reproductive body : first, the aerial spores or 

 couidia, produced in enormous quantities in spring and early 

 summer ; second, following these, small blackish receptacles, more 

 or less spherical in form, and visible to the naked eye, containing 

 naked spores, produced by the hyphse lining the receptacle, these 

 spores being of two different kinds ; and finally, in the same or 

 different receptacles, small sacs or asci arising from the base of 

 the cavity and containing a definite number of ascospores ; these 

 are usually brought to maturity during the course of the winter, 

 and, germinating in the spring, complete the cycle by producing a 

 mycelium and conidia. Such a perfect course of development is, 

 as I have said, hardly normal. In the majority of cases the 

 ascosporic stage is either very rare, or has been totally eliminated, 

 the aerial conidia alone are known, and sj^stematic students are 

 compelled to group these forms by themselves, as though they 

 were separate and distinct species, remaining content with 

 classifying such imperfect forms under "form-genera" and "form- 

 species." So also in many cases only the perfect or ascosporic 

 condition is known ; in fact it is rare to find a fungus of this 

 group in which the complete life-history is known, though every 

 year sees some form-species properly transferred to the perfect 

 fungus of which it is merely a condition. 



Before leaving this portion of our subject I must mention at 

 least three other groups of fungi, which almost invariably exist as 

 parasites upon the higher plants and are therefore of great interest 

 to the vegetable pathologist. We have considered the Basid- 

 iomycetes or Mushroom group, in which all trace of sexual 

 reproduction is lost ; and the Ascomycetes, in which, roughly 

 speaking, the spores are born free in the air on special stalks, or 

 enclosed in sacs or asci contained in special receptacles, which 

 may arise as the result of a more or less sexual process of 

 fertilization. Between these two groups, and in a manner 

 connecting them, are two smaller groups — the Ustilagiueai and 

 the Uredineae, the former including the so-called ^^ Smnts," and 

 the latter the ^^ Rusts." The Ustilaginefe are characterized by 

 their inconspicuous mycelium and the incredible number of spores 

 produced, as well as by certain peculiarities in their development 



