210 BOTANICAL GAZETTE [MARCH 
some of the species is distinctly advantageous to the dominant 
plants, while that of others is just as distinctly disadvantageous, 
as for example the parasitic fungi, but they are all presént because 
the dominant plants have made it possible by their control of the 
environment. In the human community we find a well marked 
division of labor among the individuals of the dominant species; 
some are engaged in supplying food, others in supplying clothes or 
fuel, others in administering the law, etc. In the plant community 
we find a somewhat comparable division of labor among the various 
species of the community, but not among the individuals of the 
dominant species. The function in the community of all members 
of the same species is the same, but some species have the function 
of manufacturing food, some for supplying a ground cover to check 
evaporation from the soil, some to act as scavengers in getting rid 
of dead bodies, etc. Another important difference between the 
human community and the plant community should be kept in 
mind. In the human community there are ordinarily more or 
less definitely organized activities carried on for the good of the 
community as a whole. On the other hand, in ‘the plant com- 
munity there is no altruism. It is a case of every plant for itself. 
The activities of certain species do result advantageously for the 
community as a whole, but this is due to chance circumstances, 
and the activities of course would be carried on just as vigorously 
if they were resulting in harm to the community. This funda- 
mental difference between the two communities, however, is the 
natural result of the presence of consciousness in the human species 
and the lack of it in plants, and as soon as we leave that fact out of 
consideration the two types of communities become strikingly 
similar. 
The individuals of any species, whether a dominant or a secon- 
dary species in a plant community such as the one we are consider- , 
ing, all make similar demands upon the environment. For this 
reason their relations seldom result in any benefits, but on the other 
hand there is constant competition between them for space, food, 
and often for other environmental factors such as light or shade. 
This is often just as true of individuals of different species which 
make such similar demands upon the environment as to merit 
being called ecological equivalents. Species which are ecologically 
