THE RED SPIDER ON COTTON. 31 
From Table VI it is seen that the shortest period of submergence 
that will suffice to kill all red spiders is 9 hours. All individuals sur- 
vived a submergence of 24 hours, and 50 per cent revived after an 
exposure of 8 hours. 
Observance of water dispersal in the fileld.—The actual dispersion of 
red spiders by surface water has been observed repeatedly in the field. 
In Plate VII a typical case of this sort in a cotton field is illustrated. 
The primary source of dispersion consisted of cultivated violets 
erowing in a dooryard, indicated by A. Upon becoming over- 
crowded a migration took place from these plants which brought 
many of them across the street (6) and into the cotton field (so indi- 
cated), where they became concentrated at (C), the point nearest to 
the violets. This infestation, limited to one end of the field, is indi- 
cated by ringed stalks. The heavy rains dislodged great numbers of 
red spiders and carried them along in the little streams which ran 
between the cotton rows. This surface water converging at the 
lowest point of the field, a large percentage of the stranded mites 
revived and reestablished themselves upon the cotton plants imme- 
diately at hand. Thus, at D there began a secondary development 
which tended to spread throughout the field. Naturally this dispersal 
is repeated with each heavy storm, with the result that these concen- 
trations at the lower points of the fields become more and more 
severe. 
Not all of the mites which are conveyed by the surface streamlets 
reach the ground through the effect of rains, as many are dislodged 
by fallmg leaves, through the weakening effect of heavy infestation, 
or by early frosts. 
PLANT TO PLANT TRAVEL. 
It is commonly the case during times of severe infestation that 
mites spread directly from one plant to another through the inter- 
lacing of branches. Such dispersion is facilitated by the close plant- 
ing of cotton and, inversely, is discouraged by wide spacing. It is 
difficult to say whether dispersion is accomp'ished more by means 
of ground travel or by leaf to leaf travel. 
WIND DISPERSAL. 
Several investigators have suspected that red spiders may be con- 
veyed considerable distances by heavy winds, but it remained for 
Mr. KE. E. Munger, of California, to conduct serious tests during 1913. 
He employed sticky fly paper at different heights above the ground 
and at varying distances from the source, which happened to be a 
badly infested almond orchard. Mr. Munger found quantities of 
mites on the sticky surface placed under the following conditions: 
Twelve feet from the ground and 100 feet from the orchard, 30 feet 
from the ground and 250 feet from the orchard, and 50 feet from the 
