364 Proceedings of the Royal Society of Edinburgh. [Sess. 
to hatch, in order to determine the proportion of sistens and progrediens 
in each egg-cluster. In every case the experiments were supplemented by 
numerous observations on the experimental area. 
The experiments to determine the value of the fumigation of coniferous 
nursery stock as a method of control were carried out in the following 
way : — A strong wooden box was procured and placed on one of its narrow 
ends. Two small apertures were cut, one on the top to allow the gases to 
escape after the experiment, and another in one of the sides, near the base, 
to allow the chemicals to be introduced after the front lid had been screwed 
on. A piece of glass was fitted into the top aperture and a wooden door 
into the side one. The box was then lined with heavy packing paper. 
A tray to hold the plants was fitted into the box. The following conifers 
were fumigated : — 
Spruce ( Picea excelsa), 2 year 2 year old,* very badly infested with 
fundatrices of a Chermes s. str. species. 
Larch ( Larix europoea), 2 year 2 year old, very badly infested with 
colonici of Cnaphalodes strobilobius. 
Pine ( Pinus sylvestris), 2 year 1 year old, badly infested with colonici 
of Pineus pini. 
Fifteen plants of each kind were placed on the tray in the box and the 
front lid firmly screwed on. The chemicals were then introduced under 
the tray through the small side aperture. After the experiment the top 
aperture was opened for ten minutes, then the front lid was unscrewed and 
the plants taken out and planted. Unfumigated conifers, infested in the 
same way as those above, were planted out on another area for comparison 
as to the effects of the fumigants on the trees. 
The effect on the Chermesidse was determined by the future develop- 
ment and egg-laying of the insects. 
The following fumigants were used : — 
Hydrocyanic Acid Gas. — This gas was generated by adding potassium 
cyanide to a mixture of sulphuric acid and water. 98 per cent, potassium 
cyanide and 66° Baume sulphuric acid (about 93 per cent, purity) are 
desirable. The proportions used were 1:2:5, i.e. 1 part potassium 
cyanide to 2 parts sulphuric acid to 5 parts water. The acid was mixed 
with the water, then the potassium cyanide immediately added. This gas 
was also generated from sodium cyanide. 126 per cent, purity is desirable 
for this chemical, and, moreover, it must contain less than 1 per cent, of 
sodium chloride. The amount of sodium cyanide used was 30 per cent. 
* Z.e., 2 years in a seed bed, then transplanted and left for 2 years. 
