l6 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
which hibernate in their respective hosts. Again, in the case of the 
finger-and-toe organism (Plasmodiophora Brassicae) Marshall Ward 
states that the plasmodium is able to pass slowly from one cell to 
another, devouring their contents. We find a similar view obtaining 
later to explain the extensive infection of potato tubers by Spongospora 
Solani, a parasite closely related to Plasmodiophora. Here, although 
the plasmodia of the non-parasitic Myxomycetes are capable of move- 
ment, it does not at all follow that those of the intracellular parasitic 
species can migrate from cell to cell and tissue to tissue, and in fact 
they do not behave in this way. Thus time after time the descriptive 
matter of " Diseases of Plants " covers a subtle passing from fact 
to theory, presenting pictures more imaginative than derived from 
actual experiences. 
A short time ago, in the Gardeners' Chronicle* a correspondent 
complained that mycologists could not yet distinguish between bitter 
pit and fruit-spot of apple. This is unfortunately true of more than 
one disease. Incomplete knowledge of the habits of fungi leads to 
confusion of symptoms. As an example we may take the case of 
brown rot in potato tubers ; much brown rot was of course known 
to be Phytophthora rot, but there were cases sometimes attributed to 
Phytophthora, sometimes to Fusarium, sometimes to no organism at 
all. After devoting some time to this matter I was able to show that 
in Phytophthora rot, or a rot due to a combined incursion of Phyto- 
phthora and bacteria, the tubers show pronounced external symptoms, 
and the fungus, or traces of its existence, can be detected in the air 
spaces ; in blotch and streak, where a bacterial factor is suspected, 
external symptoms are rarely presented, but the flesh is peculiarly 
marked ; in both these types wound cork is formed, whereas in 
" bruise," often wrongly held to be an after-effect of Phytophthora 
attack, wound cambium does not arise. In the last case the diseased 
areas possess a grey or black coloration and the cells appear to be 
progressively poisoned. Many other so-called diseases also need 
analysis ; for example, in fig disease what is the relation between shoot 
die-back, cankered branches, and the strangely mottled leaves, or in 
peach what connexion is there, if any, between the shoot die-back 
and curl ? 
There are several problems under investigation in other countries 
that need study here in special relation to the conditions obtaining 
in this country. Amongst these a disfigurement of apples, especially 
of dessert varieties — the apple fruit-spot to which I have just referred 
— claims serious attention. This spot or blotch has exercised 
mycologists in the United States for many years, and several bulletins 
have been issued both from the Bureau of Plant Industry and the 
Experimental Stations of the chief States in the Union. In several 
cases the trouble has been attributed to fungi such as Sphaeropsis 
Malorum Berk., species of Alternaria, Phoma Pomi Passer. (=Cylindro- 
* See Gardeners' Chronicle, November 28, 1914. 
