252 ReEporT OF THE HORTICULTURAL DEPARTMENT OF THE 
by the germinating spores of fungi bring about changes, the most 
important of which is the bringing into solution of small amounts 
of copper. Since the mixture is brought into a fine state of division 
in spraying, the above changes take place very rapidly on foliage 
where atmospheric agencies have easy access to the small particles. 
In this condition the copper is especially easily acted upon by the 
carbonic acid in the air and more or less of it is dissolved. 
THE TOXIC ACTION OF BORDEAUX MIXTURE. 
The toxicology of bordeaux mixture in relation to both fungi 
and host has been studied by many investigators, chief of which 
are Rumm,®” Fairchild,®?®§ Zucker,®?? Swingle,*®? Aderhold,*! Miani,# 
Clark,4#* Bain,“* and Schander.” Space does not permit a dis- 
cussion of the theories set forth by these investigators and ] am 
able to present here but a brief summary of their conclusions. 
The results of investigation in this field may be roughly grouped 
into two classes. 
I. Small quantities of copper are dissolved by rain, dew, or a 
moist atmosphere and pass through the epidermis of leaf or fruit 
to the interior with harmful effects. 
Bain*® seems to have been the first worker to present evidence 
in support of the above theory from direct experimentation though 
other writers had suspected the part played by meteoric moisture. 
Bain states his conclusions drawn from carefully conducted ex- 
periments on peach foliage as follows: 
“tz. Bordeaux mixture and pure basic copper produce no injury 
to peach foliage if no liquid water accompanies them. 
“2. In a saturated atmosphere, where water is not deposited on 
the leaves, there results no injury from bordeaux mixture, and 
but little from pure copper hydroxide; this injury is also probably 
less than in a dry atmosphere under like conditions, even if water 
be present. | 
“3. When protected from direct sunlight even the presence of 
water does not call forth this injury to peach foliage; but whether 
its immunity under these conditions is due to less light, less heat, 
or absence of strong air currents, or to the combined action of all 
these circumstances does not appear from these investigations. 
_*"Rumm (48 49, 50,. 51). ™ Fairchild (20, p. 26). ™ Zuckerset Gee 
“ Swingle (60, p. 21,33). “ Aderhold (1). “ Miani (39). 
“ Clark (13). “ Bain/(4).5, 9? Schander C54) 
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