136 
JOUKNAL OF THE ROYAL HOETICULTURAL SOCIETY. 
the case of the former the leaves were more or less affected by the fungus, 
not a fruit in the whole crop (according to the testimony of the gardener 
who had personally gathered the fruit) showed any signs of the mildew. 
Mr. George Massee informs me that the Strawberries in the neighbour- 
hood of Yarmouth suffered very severely from the attacks of the mildew, 
the crop in many cases being rendered unmarketable, and that here also 
the fruit of the ' Royal Sovereign ' was found to resist the disease. 
A correspondent from Bedfordshire reports : We have never before 
had a general attack of mildew as in the present season. It has generally 
been confined to ' Black Prince ' and allied varieties. ' Sir Joseph Paxton ' 
is also subject to attack on some soils and in certain seasons. I saw a 
curious instance lately of the special liability of certain varieties to 
attacks of the mildew — a bed of ' Viscountess H. de Thury ' had a few 
plants of ' Paxton ' growing amongst them, and in every case the 
* Paxtons ' were badly mildewed while the others were quite free." 
Berkeley (1) noticed ihat, while the crop of ' Cuthill's Black Prince ' 
was destroyed, plants of ' Keens' Seedling,' standing on the same shelf as 
the former, remained perfectly free. 
Professor J. C. Arthur (3) has also recorded that, while the ' Jucunda,' 
^ Mount Vernon,' 'May King,' and ' Garretson ' were attacked, other 
varieties nearly or wholly escaped. 
Climatic Conditions favourable to the Disease. — As regards the 
climatic conditions favourable to the appearance of "the disease, there 
seems to be a consensus of opinion among gardeners that these are to be 
found in sudden alternations of temperature, especially a decrease of 
temperature during the night, or a cooler temperature caused by rain 
followed by hot sunny weather. 
Some experiments I have made on the germination of the conidia 
seem to give some evidence on this subject. Conidia sown in hanging 
drops of water at ordinary temperature were found to germinate very 
unsatisfactorily, only a few of the conidia producing short germinal tubes. 
Various media were used, but with no better success. It then occurred 
to me to try the effect of a low temperature on the germinating powers 
of the conidia. I was led to do this from the remarks of many observers 
on the subject of the general conditions favourable to the appearance of 
mildew on plants. Thus in the Report of the Commissioner of Agri- 
culture for 1885, p. 89 (Washington), it is stated: "There is much in 
connection with the appearance of mildew on the foliage of plants which 
w^ould indicate that it is in most cases the result of cold or aridity in the 
atmosphere, or perhaps rather in their combined action." It has, too, 
been frequently asserted by horticulturists that cold draughts of air will 
bring on mildew to Roses. Further, Eriksson had already experimented on 
these lines with regard to the germination of U redo spores, and reached 
the conclusion that " it must be regarded as proved that cooling down to 
near freezing-point, or even to a few degrees below freezing-point, has a 
favourable influence on the germination of the Uredo spores " of certain 
species of " rust," " at least in the condition in which they occur in the 
open during the warm summer months." 
In the experiments on the present fungus. Strawberry leaves covered 
with conidia were subjected to a temperature of 0° C. for twelve hours. 
