11 



of which thoroughly and completely is almost impossible, especially 

 after the trees hav^e attained any size. Furthermore, with gas there is 

 no danger of spotting the fruit as may happen with improper sprajdng. 



Fig. 4. — Removing tent by horse power. 



The more straggling growth of the lemon makes gassing less necessary, 

 notably where the open system of pruning is adopted. 



Successful as gassing is, it is not effective in the same degree against 

 all the scale insect enemies of citrus plants. It is especially A'aluable 



Fig. 5. — Series of tents for continuous operations. 



against the black scale and the red scale of California, but with such 

 of the armored scales as are oviparous, or deposit beneath the old 

 scales eggs wliich undergo a certain amount of incubation before hatch- 

 ing, gassing ie not alwaj^s effective. Under such circumstances the 



172 



