DEFINITION OF THE PARASITISM OF FUNGI. 6 



of boring through cell-walls, if the part be impregnated with a 

 stimulating Solution. They behave here completely as parasites. 

 For example, hyphae of Penicillium glaucum penetrate into living 

 cells of a leaf injected with a two per cent, solution of cane 

 sugar, while without previous injection of the leaf they have 

 never been observed to do so. Penicillium is also known, in 

 certain circumstances, to become parasitic. 



Many species of fungi are capable of passing the whole or a 

 part of their life as parasites on living plants. Conspicuous in 

 this respect are the Uredineae and Ustilagineae, many Ascomy- 

 cetes, including all Exoasceae and Erysipheae ; and amongst the 

 lower fungi, most of the Chytridiaceae and all the Peronosporeae. 

 Nor does this exhaust the list, for amongst the remaining fungi 

 we may find isolated families, genera, and even species occurring 

 as parasites, while forms closely related to them are saprophytic. 



To classify the parasites, saprophytes, and intermediate forms, 

 we shall adopt that arrangement proposed by Van Tieghem and 

 De Bary. 



§ 2. CLASSIFICATION OF PARASITES AND SAPROPHYTES. 



1. True saprophytes are such as regularly pass through their 

 whole life-history in a saprophytic manner. They may derive 

 their nourishment from different kinds of pabulum, or be limited 

 to some definite substratum. The true saprophytes do not come 

 within the scope of this book.^ 



2. Hemi-saprophytes (the 'facultative parasites' of De Bary) 

 are wont to pass through their whole development as saprophytes, 

 but on occasion are capable of existing wholly' or partially as 

 parasites. Amongst them are included particularly such species 

 as may be designated " occasional parasites," which commonly 

 occur as saprophytes, and only under certain conditions become 

 parasitic. 



3. True parasites (the 'obligate parasites' of De Bary). These 

 undergo no part of their development as saprophytes, but live in 

 every stage of existence as parasites. 



4. Hemi-parasites (the 'facultative saprophytes' of De Bary) 

 are capable, if need be, of becoming saprophytes for a season 



'Johow proposes the term Holo-saprophytes for those non-ohlorophyllous 

 Phanerogams which live exclusively saprophytic on organic debris, in contrast 

 to those possessing chlorophyll, which he names Hemi-saprophytes. 



