148 FUMIGATION METHODS 
packed, but laid loosely upon trays in the fumigating 
box or room. ‘The details of making and handling 
the gas are the same as that for nursery stock and 
greenhouse work. ‘The apparatus’ to be used will 
depend upon the number of plants grown and handled 
annually. A convenient box for fumigating straw- 
berry plants is shown in Fig. 71. 
Experimental and praétical tests—At the Dela- 
ware Experiment Station a very complete series of 
tests were started by Prof. G. Harold Powell and 
completed by Prof. E. Dwight Sanderson. Several 
infested plants were fumigated and placed in paper 
bags, where they were left and examined twelve hours 
jater. The following amounts of cyanide were found 
sufficient for the destruction of the root-louse: One- 
tenth gramme (0.1) per cubic foot space, exposed 
twenty minutes; fifteen-hundredths (0.15) gramme for 
fifteen minutes; two-tenths (0.2) gramme for ten min- 
utes; three-tenths (0.3) gramme for five minutes. In 
the same series where 0.3 gramme cyanide was used, 
all the lice were killed where the exposure was only 
five minutes. Itis not desirable to use these larger 
amounts even for a short exposure. The work by 
Professors Powell and Sanderson corroborates the vari- 
ous tests of the writer that the two-tenths gramme 
formula is satisfactory when properly handled. Under 
some circumstances a few lice may be secreted among 
the crown leaves and possibly escape where large num- 
bers of plants are fumigated. This danger can be 
overcome largely by loose packing before fumigation. 
Praétical tests;—Early in April Professor Sanderson 
