THE ORCHID REVIEW. 19 
apex of the dorsal is peculiar. The infl is ionally two- 
flowered, as in the present example. 
Thus the history of this group of plants is particularly interesting, and if 
the last- named i is neath of great decorative value it should find a place in all 
C. X siamense most resembles this parent, but 
the dorsal sepal, especially, is much modified; and it is a more attractive 
plant. All three usually flower in the winter or early spring. 
4 
THE SPOT DISEASE OF ORCHIDS. 
A VERY important paper on the above disease, by Mr. G. Massee, of Kew, 
appears in the last number of the Annals of Botany (vol. ix., pp. 421-429, 
t. 15), in which the vexed question of its origin is set at rest. Allusion was 
made to the matter at page 130 of our last volume, but it now appears 
that the disease is not due to a fungus, as was then supposed, but to causes 
which to a great extent are under the control of the cultivator. The 
investigation was at first d with the p ived idea that a 
fungus was the cause of the mischief, but when various experiments had 
failed to demonstrate its existence a search was made for bacteria, and with 
like results. Efforts were then made to induce the disease in healthy plants 
by inoculation with the expressed juice from diseased spots, but with no 
more success, and this was accepted as evidence that the malady was of 
non-parasitic origin. 
It has often been contended that ‘spot’ was due to atmospheric con- 
ditions, and Mr. Watson now suggested a sudden chilling of the plants as a 
probable cause. Experiments were therefore made with a view of testing 
this. A plant of Habenaria Susanne, perfectly free from spot, which had 
been growing in a temperature of 75° to 80° F., was covered with a bell- 
glass, on which cold water from a tap was allowed to flow for twelve hours, 
during which time the temperature under the glass ranged between 41° and 
45° F. Some minute particles of ice on one occasion had first been placed 
upon the upper surface of the leaves, and on a later one some mhate 
drops of water. Twenty-four hours after the 
examination showed that wherever a minute drop of water had eee 
whether formed by melting of the ie of ice or not—a diseased as 
appeared, showing all the mi istics of true ‘spot,’ but 
wherever the leaf remained dry no er damage was observed. These spots 
were examined at intervals, and within four days every phase of the disease 
was observed. Additional experiments showed that a fall of at least 9° F. 
from the previous average was required to induce the formation of ‘spot,’ 
and consequently that plants previously grown in a high temperature were the 
