148 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



example, the sepals are much sooner and more easily injured 

 than the upper petals and labellum. Microscopic examination 

 shows that whilst stomates are frequent on the sepals of both 

 plants, the petals have relatively few, comparing equal areas of 

 surface. The labellum of Cattleya in many cases was found to 

 be destitute of stomates. This part is usually the last to show 

 actual injury. The action of the stomates here is probably to 

 afford increased access of sulphurous acid to the part, which then 

 directly attacks the soft, unprotected cells within. 



The effects of a slow current of fog, and of sulphurous acid 

 of various dilutions, upon living protoplasm have been very 

 carefully followed under the microscope. The procedure in both 

 cases was identical. A slow current was drawn by aspiration 

 through a specially devised chamber on the stage of the micro- 

 scope. The transparent root-hairs of Limnobium with their 

 actively rotating protoplasm, and portions of the leaf of Vallis- 

 ncria, were chiefly used. The effect of dense fog resembles that 

 of dilute sulphurous acid. The rotating protoplasm is found 

 gradually to swell up and invade the vacuole, its defined margin 

 becoming less and less distinct. Finally, the protoplasm becoming 

 granular, breaks down entirely ; the rotation during the process 

 gradually slowing, ultimately ceasing. The whole process with 

 fog occupies several hours. This line of research, to which I 

 attach importance, will be continued during the summer with 

 sulphurous acid and other substances. 



A considerable series of experiments has been made in the 

 closed chamber, which was constructed for this, as also to serve 

 as a fog-proof chamber for cultural purposes. As a fog-proof 

 chamber it has not been used so far. At an early period I 

 found that certain defects which could not be remedied forthwith 

 disqualified it for this purpose. Since then it has served as a 

 closed experimental case, in which plants were exposed to 

 sulphurous acid gas of varying strength. It was possible also 

 to draw off a current of the special atmosphere, to which the 

 plants in it were exposed, and study its action upon living pro- 

 toplasm under the microscope. A comparison could thus be 

 effected between the macroscopic and microscopic phenomena 

 simultaneously. The amount of sulphurous acid present was 

 under control, and frequent estimates of its amount were made 

 by aspirating air from the chamber through permanganate, the 



