SAPROPHYTISM AND SYMBIOSIS 323 
into sauerkraut, the numerous slime-molds (Myxo- 
mycetes), and various other forms, which are more or 
less intimately connected with human industries, or with 
public or private hygiene. 
Humus, one of the most important compounds of soil, 
is composed almost entirely of the remains ot plant 
and animal bodies in various stages of disintegration, 
FIG. 230. Indian pipe (Monotropa uniflora). (Photo by Elsie M. 
Kittredge.) 
and the disintegration is caused, almost entirely, by the 
action of enzymes secreted by bacterial and fungal 
saprophytes. Thus we come to realize that these sapro- 
phytic plants are absolutely essential to the most funda- 
mental of all human occupations, namely agriculture. 
304. Saprophytic Flowering Plants. Not all sapro- 
phytes are fungi. The Indian-pipe (Monotropa uniflora, 
