MacDougal. — Symbiotic Saprophytism. 39 
changes in the metabolic activity of the protoplasm as a body. 
The passage of ‘ organic ’ substance through typical ecto- 
plasmic layers is admittedly accomplished with difficulty, 
and the modifications to facilitate absorption would consist 
in alterations of the diosmotic properties of the limiting 
membranes, rendering them permeable to such substances, 
or promoting the transmission of the ions of a substance 
separately ; or in such changes in character as to enable the 
membranes to unite with compounds yielding them internally, 
in their original form ; or in the formation of special canals 
for chemical transmission ; or in the establishment of electro- 
lytic action, or a degree of potential that would facilitate 
absorption (Pfeffer, 30). On the other hand, the essential 
feature of saprophytism may consist in the ability to use 
feebly oxidized bodies such as are utilized by Fungi. It 
is indeed probable that saprophytism implies modifications 
along several of the lines indicated. The saprophytic adapta- 
tion is highly characteristic of the Fungi, and physiologically 
must be but little removed from parasitism so far as the 
nature of the adaptation is concerned. 
The Fungi are often united with other forms as parasites 
and in a manner in which the second plant also receives some 
benefit. The union of Fungi and Algae in this manner has 
resulted in the formation of certain definite types of morpho- 
logical constitution of such constant character as to constitute 
a distinct taxonomic group, the Lichens. In symbiotic unions 
with Pteridophytes and Phanerogams, the higher plant, by 
reason of its superior organization and greater physiological 
inertia, has retained its individuality more nearly, and the 
association results only in modifications of certain organs. 
It is difficult to account for the origin of mycorhizal arrange- 
ments. Presumably Fungi are attracted to the bodies of 
other plants chemotropically, and in both parasitism and 
symbiosis it has formed coating mycelia, and has penetrated 
into various tissues in different plants. The critical fact, 
however, which resulted in the absorption of material from 
the higher plant by the parasite, or set up an interchange 
