374 
The Study of Plant Diseases. 
siderably more in the space of a month, than could have been done 
by our unaided efforts, 
DESCRIPTION OF PLATES III. & IV. 
Illustrating The Messrs. West’s Paper on the Ecology 
of the Upper Driva Valley in the Dovrefjeld. 
Plate III. 
Fig. 1. The exposed rocks near the road (marked “ R” in the chart). 
Fig. 2. The alpine shrubland on Knutsho at 4,000 feet, consisting mostly 
of “ grey willows,” Betula nana, and Juniperus nanus. 
Fig. 3. Sand bank near the river Driva covered with Phleum alpimnn. 
Plate IV. 
Fig. 1. The lichen-formation at the head of the valley in which there is a 
considerable admixture of stunted shrubs of Betula nana and Juniperus nanus. 
Fig. 2. Lychnis alpina in the lichen-formation. 
Fig 3. The crustaceous lichens on a vertical rock face on one of the lower 
slopes of Knutsho. A single specimen of a sp. of Gyropliora is visible in the 
picture. Note that the entire rock surface is covered with the prolific growth of 
lichens. 
THE STUDY OF PLANT DISEASES. 
[The following notes on some phases in the present day investi¬ 
gation of plant diseases have been written in the hope that they may 
prove of interest to botanists who are not primarily concerned with 
mycological research.] 
LTHOUGH some work had been done by Berkeley and others 
on diseases of plants prior to 1865, the critical study of 
certain groups of fungi as disease-producing organisms may be 
said to date from De Bary’s observation in that year of the 
penetration of a host plant by the germ tube of a fungus spore and 
the subsequent development of a mycelium within the tissues. The 
clear establishment of the parasitism of certain fungi by this and 
similar observations gave an immense impetus to the study of 
fungi as agents in the production of disease amongst the higher 
plants. When one recognises that there is scarcely a plant of 
economic importance which is not subject to one or more serious 
diseases caused either by fungi or more rarely by bacteria, the 
importance of the study of mycology becomes manifest. From 
Rust in Wheat to Mildew on Vines and from Scab in Potatoes to 
Canker of Larch trees the story is always one of severe economic 
