December, ’23] 
woglum: hydrocyanic acid gas 
519 
control the cottony cushion scale with sprays. In its earliest stages, 
the gas process was interesting rather than fully practical. The tents 
were bell-shaped, very heavy, sometimes oiled, and almost gas tight. 
Very cumbersome equipment was used to move these tents over trees. 
The process was slow and necessarily expensive. The generation process 
of concentrated acid slowly dropping onto dry cyanid, or into a cyanide 
solution was prolonged and somewhat uncertain of uniformity. 
By the early nineties, fumigation had undergone vast improvement. 
The heavy bell-shaped tents had given way to flat octagonal sheets of 
untreated tightly woven canvas. The advent of flat sheets which could 
be moved by two poles greatly simplified the covering and reduced the 
cost of the operation. The simple pot method of generation, which 
consisted of dropping solid cyanide into a dilute acid had come into use. 
Day fumigation had given way to night fumigation, which meant less 
plant injury. The greatest weakness of the system at that time was 
the lack of an accurate and practicable method of estimating the dosage, 
and this condition was reflected in one way or another throughout the 
first 20 years of orchard fumigation, at times receiving no small amount 
of attention from California investigators, particularly Woodworth. 
Nevertheless, the system as a whole proved sufficiently satisfactory 
that it rapidly became the standard of scale-insect control in California, 
a position maintained up to the present time. From 1893 to 1907, there 
was no outstanding development in orchard fumigation other than in 
increased volume of work done. Conflicting ideas between fumigators 
on dosage, exposure, proportion of chemicals and general procedure, 
however, became numerous. 
The last fifteen years have seen the greatest progress made and the 
most rapid changes in fumigation since its earliest days. The develop¬ 
ment by Morrill in 1907 of a practical method of marking tents for the 
calculation of dosage was the most important step toward accurate 
orchard fumigation. The writer introduced this marked tent method 
of fumigation into California in 1908, strengthening it by a dosage sched¬ 
ule adapted to the fumigation of any citrus tree pest against which fumi¬ 
gation is practiced. The superiority of the marked tent system with 
its sliding scale of dosages rapidly became apparent to growers and 
fumigators alike and for the last decade has completely supplanted all 
other methods wherever orchard fumigation is practiced. 
Potassium cyanide exclusively was used in fumigating up to 1909. 
The work in 1908-09 of Woglum and McDonnell showing the availability 
of high grade sodium cyanide for fumigation formed the basis of con- 
