426 Mas see. — The ‘ Spot 3 Disease of Orchids. 
from a tap allowed to flow over the bell-jar for twelve hours, 
during which time the temperature inside the jar ranged 
between 41 and 45° F. Twenty-four hours after the experi- 
ment, the points on the surface of the leaves originally covered 
by particles of ice were pale in colour, and on examination 
under the microscope, plasmolysis of the cells of the palisade- 
tissue, and degeneration of the chloroplasts were found to 
have taken place. The remaining spots were examined at 
intervals, and within four days every phase of the disease was 
observed, agreeing in every respect with the features already 
described. 
The foregoing experiment showed that a sudden fall of 
30° of temperature could not induce ‘ spot ’ on the dry surface 
of the leaf, but only at those points where it had been 
moistened by the melted ice. That the chill caused by 
contact with the ice itself was not necessary for the formation 
of ‘ spot 3 was proved by a second experiment with the same 
species of plant, all the conditions being as nearly as possible 
counterparts of those in the first experiment, excepting that 
minute drops of water at a temperature of 45 0 F. were placed 
on the leaves instead of particles of ice. A diseased spot 
appeared at each point previously occupied by a drop of 
water, and showed all the microscopic characteristics of true 
‘spot. 3 Numerous additional experiments, with the object of 
determining the minimum depression of temperature necessary 
to produce the disease, showed that the formation of ‘ spot 3 
could not be induced by a fall of less than 9 0 F. from the 
average temperature in which the plant had been previously 
growing. One other point in regard to temperature was 
clearly demonstrated by the experiments, viz. that plants 
which had previously grown in a high temperature became 
diseased at a much smaller reduction of temperature than 
plants previously accustomed to a comparatively low tem- 
perature. 
In conducting the experiments described above, irregularity 
in the appearance of the spots in different specimens of the 
same species, even when conducted under precisely similar 
