New York AGRICULTURAL EXPERIMENT STATION. 269 
which has to do with bordeaux injury is of quite a different 
'nature. Moisture is necessary, whether meteoric, secreted by 
_ the host plant, or from whatever source, for the germination of 
the spores of fungi. It is always an accompaniment of bor- 
deaux mixture in the destruction of germinating spores. It is 
the presence of this moisture with bordeaux mixture, in greater 
or less quantities, that becomes a prime factor in bordeaux 
injury. : 
Attention has already been called to the anomalies of bor- 
deaux injury. The influence exerted by moisture explains many 
of them. The fact of injury or no injury is for most part de- 
pendent upon rain or dews; the degree of injury is likewise so 
dependent; this factor controls the length of time after spray- 
ing at which injury appears, whether one or several weeks. 
Different sets of conditions are brought about if the moisture 
comes as a dew, a fog, a mist, a shower, or as a torrent. If the 
tain be accompanied by wind, parts otherwise protected may 
be injured. Sunlight makes a difference in degree of injury 
largely because of its influence on external moisture and leaf 
secretions. It is probable that temperature exerts a similar 
influence. 
There is still another influence of wet weather that demands 
attention; namely, its effect upon the parts of the host plant in- 
jured by bordeaux mixture. 
It is reasonable to suppose that leaves and fruit have less 
resistant power against the action of copper poisons when wet 
weather prevails than during dry weather; for it is a matter of 
common botanical knowledge that green plant organs are more 
succulent, their epidermis thinner, and more tender in wet 
weather than in dry. Kohl® found “the cuticle to be much 
thinner when the plant is grown in a moist atmosphere;” 
Lothelier® that it may entirely disappear when grown in a 
saturated atmosphere. Bain’ shows remarkable differences in 
the cuticle of the apple and peach leaves in accordance with 
weather. His conclusions are: “The cuticle of the apple leaf, 
and especially that of the peach leaf, shows in common with 
other plants considerable variations in thickness, dependent on 
the medium in which +he leaves are developed; exposure to a 
dry atmosphere, to strong air currents, in short, to all the atmos- 


n> awonle ¢ 33). 
_™Lothelier (38). 
* Bain (4, p. 67). 
