1887. ] BOTANICAL GAZETTE. 181 
to accept, at least, a mechanical symbiosis of unicellular alge 
and animals in a considerable number of instances. Whether 
the svmbiosis is physiological as well as mechanical is a point 
on which more light is apparently needed. 
The svmbiosis of plants, and animals is, perhaps, better 
‘o be compared with that of Nostocs with Hepatice and 
- -Azolla than with the condition which exists in lichens. Some 
of the recorded cases show clearly a mechanical symbiosis, 
even if others be regarded as merely accidental and tempo- 
rary unions of different organisms. Whether the symbiosis 
here is physiologically of advantage to both organisms is 
doubtful. he Nostocs are certainly not injured, and they 
may derive benefit from the shelter afforded. It will not do 
'0 go too far in this direction, however, because we should, 
at length, be forced to speak of symbiosis in cases where 
i d 
biosis because, as it seems to me, botanists have gone too far 
In assuming a beneficial action of the parasite on the host in 
Accepting the existence of symbiosis where both members 
are chlorophyll-bearing plants, we must still believe that, 
ith rare exceptions, the cases where one member is a 
fungus should be referred rather to the class of true parasites, 
m which the advantage is altogether on one side. 
f we turn now to the question of the origin of vegetable 
Parasites we find ourselves in a dilemma. Certainly, the 
Parasites could not have originated before the plants and 
‘nimals on whose remains or in whose tissues they live. On 
the other hand, accepting the law of evolution, that the more 
