go The Botanical Gazette. [March, 
the effect of lenses, by which the sunlight became concen- 
trated and thereby caused a burning of the exposed parts of 
the leaves. Another theory, quite generally adopted, was 
that drops of water left on the leaves after they had been 
watered, might have the same effect as lenses or by their 
own heat be able to burn the leaves, especially in houses 
without sufficient ventilation. 
De Candolle suggested that the burning might be caused 
by the drops of water, which at once softened the tissue of the 
leaves, became heated in the sunlight and thereby prevented 
evaporation. In Gardener's Chronicle for 1858 burnt spots o” 
orchids were said to originate from too much moisture Mm 
connection with too low temperature. ; 
he explanation most commonly adopted, however, is that 
which attributes the effect to drops of water having been 
heated by the sunlight and it has been so recorded in the 
more prominent phytopathological manuals. Sorauer for ie 
stance in his Pflanzenkrankheiten explains the fact quite — 
briefly by this statement. Neumann! came to the same col 
clusion by some experiments he made with Cordyline. Of 
‘Adansonia, Vol. II, 1862, p. 312. 
?Die Krankheiten der Pflanzen, 1880, Pp. 174. 
*Samenbruch bei der Weinbeere, Botan. Zeitung 1872, p. 113. 
‘Ueber den Sonnenbrand der Rebenblztter, Die Weinlaube 1886, p: 499 
