388 Massee : Fungi from Various Standpoints. 
great importance, the annual loss caused by these diseases 
being very considerable. 
We do not yet however know enough of the life histories 
of parasitic fungi. We know parts or stages, but not always 
the entities or complete life-cycles. There are many ways 
in which we could attack the subject of plant diseases and the 
problems presented by them. The distribution of spores, 
for instance, is important. The methods of spore distribu- 
tion are very various, among other agents being wind, insects, 
animals, etc., man himself often contributing. European 
plants conveyed to different parts of the world invariably 
carry their fungal diseases with them, and often with change 
of habitat the latter become far more virulent. Sometimes 
the seed only is imported and yet the disease manifests itself. 
As instances, potatoes, French beans, etc., have been intro- 
duced into Nyassaland and other places, and after a time 
those diseases known at home manifested themselves. I am 
in agreement with Eriksson’s theory that the seed contains 
what is known as mycoplasm, which after a time — given 
favourable conditions — develops into mycelium. This is not 
generally held in this country chiefly through experiments made 
by Marshall Ward, who disproved it to his own satisfaction. 
Eriksson however, holds that propagation by spores alone is in- 
adequate to account for the enormous simultaneous outbreaks 
of rusts such as have occurred for instance in the great plain 
of the Ganges in India and elsewhere, over very wide areas. 
Experiments I have made show that spores are mostly 
liberated during the day, but infection takes place most readily 
during the night. The latter is on account of the presence 
of dew, moisture being an essential condition for spore germ- 
ination. 
Physiological factors are important in the question of 
whether infection takes place or not. Some plants have 
enzymes which are inimical to infection, and others have 
particular enzymes which are favourable to infection. In 
the case of the former the germ-tube of the fungus spore is 
poisoned on entering the cells of the plant not having the 
enzyme favourable to the invading fungus. 
There is no such thing as an epidemic of fungi in say a 
virgin forest, i.e., where the balance of nature is undisturbed. 
Where economic plants are largely cultivated their physio- 
logical balance has been upset, and this renders them more 
open to attack ; those plants which are tampered with most 
being most susceptible to disease. 
Plant pathology is only about 25 years old. and there is 
much to learn as regards remedial measures. We have learnt 
how to diagnose a disease, and that is a good deal, but much 
remains to be done. 
Naturalist, 
