356 A DIVISION III. —MODE OF LIFE OF THE FUNGI. 
2. NUTRITIVE ADAPTATION. 
Section XCIX. Fungi have long been divided into two main sections founded 
on their nutritive adaptation Those which constitute the first category feed on living 
organisms whether plants or animals, and are termed parasites. Their relationship 
with their hosts is that of a common life, a symdzosis. The others inhabit decaying 
bodies and feed on dead organic substances, and have been named therefore since 1866 
saprophytes. The two kinds of adaptation are sharply distinguished from one another 
till we come to cases in which it may be doubtful whether a body should be said to be 
alive or dead, but with these we are not further concerned; both are distributed 
unequally amongst the different species, and are developed in varying degrees in 
different individuals with many intermediate gradations. The extreme cases and the 
first to be distinguished are species of purely and strictly saprophytic and species of 
strictly parasitic mode of life. Others lie between these two extremes ; there may be 
firstly species which both can and do normally go through the whole course of their 
development as saprophytes, but which have also the power of going through their 
course of development wholly or in part as parasites ; these may be called with Van 
Tieghem facultative parastles. Secondly, species which, as far as we know, do as a 
rule go through the whole course of their development as parasites, but at the same 
time are able, at least in certain stages, to vegetate as saprophytes: these may be 
termed facullative saprophytes. As far as we fully and certainly know, the parasitic 
mode of life is always indispensable to the complete development of this second kind. 
Keeping in view the latter circumstance we obtain the following grouping according to 
the life-condition: 1. Pure saprophytes. 2. Facultative parasites. 3. Obligate 
parasites, that is, species to which a parasitic life is indispensable for the attainment 
of their full development. The latter are again divided into (a) strictly obligate 
parasites, that is, species which, as far as we know, live only as parasites, and (b) 
facultative saprophytes. Most species in category 2 may be able to attain their full 
development in both modes of life. It is at present uncertain whether there are 
transitional forms between them and 3 (b), parasitism being the rule in some species, 
but the full development being possible in exceptional cases in a saprophytic mode of 
life ; the many gradations between them of other kinds make it not improbable. 
In presence of these gradations the foregoing division can only be a frame, such 
as is necessary for obtaining a clear survey of the phenomena, and it should be 
distinctly observed that it has in view the ascertained adaptations and arrangements 
which hold good in the natural, and, as we are accustomed to say,, the spontaneous 
course of things. There may be possibilities of existence in a species which 
transcend these adaptations. Artificial conditions may in some cases be established 
which may result, for example, in the development of a spontaneously and strictly 
parasitic Fungus in a way not parasitic, just as it is possible to rear normal bean or 
maize-plants by water-culture. We can conceive such a possibility in every case, 
even in much more difficult cases than any which occur in this work, such for instance 
as those of trichinae and tape-worms. It must also be allowed that plants cultivated 
under artificial conditions of such a kind may be of the greatest help to the under- 
standing of the phenomena. How far a state of things produced for the purpose of 
