SCIENTIFIC COMMITTEE, JANUARY 8. 



XX111 



SCIENTIFIC COMMITTEE. 



January 8, 1907. 



Mr. G. S. Saunders, F.L.S., in the Chair, and four other members 



present. 



Pleurothallis sp. — Mr. R. A. Rolfe reported that the Pleurothallis 

 shown at the meeting on November 20, 1906, by R. I. Measures, Esq., 

 could not be identified at Kew, but may be one of several described by 

 Reichenbach, still only known from description. It is near P. velaticaulis 

 Reichb. 



Grapes shanking. — Some shoots of vines, the fruit of which had 

 shanked, were received from Basingstoke. From the description of the 

 border that accompanied the specimens it was thought that the trouble 

 was undoubtedly due to unhealthy root action, and that renovation of 

 the border would probably result in improvement in the growth of the 

 fruit. 



Magnolias and Mealy Bug. — Some shoots of magnolia affected with 

 mealy bug were received from Horsham. The shoots were from plants 

 growing on the south side of a wall 200 feet long and 15 feet high, and, 

 although various insecticides had been tried upon the plants no good results 

 had followed. The scale insects were, curiously enough, not found in the 

 houses built on the south side of the wall. Mr. Saunders reported as 

 follows : — " The mealy bug attacking the magnolias is Dactylopius 

 lo?igispi?ius. Of course it is very difficult, if not impossible, to properly 

 cleanse the leaves with an insecticide, as the plants are growing against a 

 wall. It might, however, be possible to destroy them with hydrocyanic 

 acid gas if some comparatively air-tight covering could be constructed over 

 the plants, e.g. a tarpaulin or a rick cloth might be fastened with a batten 

 against the wall above the plants and allowed to fall down in front of 

 them to the ground. The sides might be fastened to the wall in the 

 same manner as the top. The gas is generated by pouring sulphuric acid 

 over cyanide of potassium. The method of procedure is as follows : Place 

 4 ounces of water in an earthenware jar, pour slowly into it H fluid 

 ounces of sulphuric acid (specific gravity 1*84), then in a shallow earthen- 

 ware dish put 1 ounce of potassium cyanide (98 per cent, strength), 

 and arrange the jar of acid so that its contents can be slowly 

 poured over the cyanide without any chance of the fumes reaching the 

 operator, as they are most poisonous. Or the cyanide may be wrapped up 

 in a piece of blotting paper and placed on a piece of board laid on the top 

 of the jar, but not closing the mouth, and by means of a stick or string it 

 may be dropped into the jar containing the acid, and then every aperture 

 should be tightly closed. The above recipe gives the quantities for use 

 in a space containing 150 cubic feet of air ; if the space be larger, the 

 quantities must be increased in proportion. The plants should remain 

 exposed to the fumes for above three hours. Means must be devised 



