190 Report oF THE BOTANICAL DEPARTMENT OF THE 
being more expensive ($60 to $75), less durable and of heavier 
draft.” 
SPRAYING BEFORE RAIN. 
“Some hesitate to spray potatoes when it looks like rain. 
They argue that the rain will wash off the bordeaux and necessi- 
tate the work being done over. Let us inquire into this matter. 
It is in rainy weather that spraying is most needed, because it is 
then that the late blight spreads most rapidly. The beating of 
the rain scatters the spores of the blight fungus and, the con- 
ditions for their germination being excellent, infection occurs 
readily. Most of the infection takes place during rainy weather. 
In dry weather the disease makes slow progress because the spores 
must have moisture in which to germinate. Moreover, much dry- 
ing kills the spores outright. 
“ Because of these facts the best time to spray is shortly before 
rain. If there is sufficient time for the bordeaux to get 
thoroughly dry on the leaves before the rain comes, it is all right. 
The leaves are then protected. Spores falling on them will be 
unable to germinate. Even when the mixture does not get dry 
spraying must do some good; but in such cases another spraying 
should be made as soon as possible. Never stop spraying because 
rain threatens. On the contrary, make a special effort to get the 
spraying done before it rains. 
COPPER SULPHATE AND COPPERAS. 
“ Many persons confuse copper sulphate with copperas. Cop- 
per sulphate is blue vitriol, also called blue stone. It contains 
copper and is used in the preparation of bordeaux mixture. 
“Copperas is an entirely different thing. It is iron sulphate. 
It does not contain copper and cannot be used for making 
bordeaux. 
“The crystals of the two substances are somewhat similar in 
appearance, but may be readily distinguished by their color. 
Copper- sulphate crystals are blue, while those of copperas are 
greenish.” 
ARSENITE OF SODA. 
KEDZIE FORMULA. 
White ‘arsenic, Pounds ss... % 0/«:c3 nh eae wie sg os 0 0: 05x eee nee 
sal; soda; pounds, ii). ody toate eaten eevee Sle) «eat. Sigler sien A ee 
Water; Gallons i. Bei 2's ale ctemiera a tee ore oo ca, ood yee 
| DD pO) 
