56 ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 
plants as the Corn-root Aphis. It is about 
one-twelfth of an inch in length, bluish- 
green and without bloom. It migrates 
from weeds to cultivated host-plants in 
summer and when abundant stunts the 
plants and causes the leaves to wither 
and finally die. Injury is heavier on 
broom-corn and sorghum than on corn. 
In Texas it has been found on barley in 
winter. Little seems to have been done 
on the control of this louse. Whale-oil 
soap 1 pound to 5 gallons will destroy 
the aphis, but it is doubtful if this would 
be practicable in the field on large areas 
SMALL GRAINS 
Three species of plant-lice, all Euro- 
pean, are injurious to small grains. These 
are: (1) the English Grain Aphis 
(Macrosiphum granarium Buckt.); (2) 
the Spring Grain Aphis (Toxoptera 
graminum Rond.); (3) the Huropean 
Grain Aphis (Aphis padi L.). These are 
all bright green forms, the first-named 
being considerably larger than either of 
the other two. In the warmer parts of 
the United States they produce parthen- 
ogenetically all the year around on grains 
and grasses, but in the North winter is 
passed in the egg stage. The injury they 
do to young grain plants is often severe, 
and grain should be watched for their 
appearance. Small localized outbreaks 
may be controlled either by plowing un- 
der, by covering the spots with straw 
and burning, or by spraying with whale- 
oil soap (1 pound to 10 or 12 gallons of 
water). On large areas of infested grain 
the only known methods of control are 
the suppression of all volunteer wheat 
and oats in the fall, late sowing of fall 
wheat, and fertilization of the soil to 
help the plants to resist attacks. 
POTATO 
The Potato Aphis 
Macrosiphum solanifolii Ashmead 
This is a large green plant-louse which 
is occasionally very injurious to‘the po- 
tato in the eastern states. The aphid 
passes the winter on Shepherd’s Purse 
and other weeds, migrating in spring 
and summer te the potato and returning 
in the fall to the weeds. The usual con- 
tact insecticides (whale-oil soap, o11 emul- 
sions and tobacco extracts) aie not prac 
ticable against this louse on a large scale 
but they may be employed with success 
on a small patch. Control on a laige 
area is reduced to clean culture, tall 
plowing and the burning over of weedy 
places in the vicinity of potato fields in 
order to clean up the land of the alter- 
nate host-plants of the aphis. 
HOP 
The Hop Aphis 
Phorodon humuli Schiank 
This is a light green non pulveluwlent 
louse originating in Hurope and now dis- 
tributed all over the United States The 
winter is passed in the exg stage on 
plums and prunes, wild and cultivated, 
the lice migrating in spring to hops In 
California researches would indicate that 
the aphis may pass its whole annual life 
cycle on the hop, as plums growing in 
the vicinity of hop-yards badly infested 
have been carefully examined and found 
to be totally uninfested by the winter 
eggs. This plant-louse may be destroyed 
hy spraving with tobacco extract (Black 
Leaf 1-2,000 to 1-8,000) combined with 
flour paste (4 pounds to 100 gallons 
water). 
W. M. Davipso~n 
Apple 
HISTORY AND ORIGIN 
The history of the apple is an interest- 
ing illustration of modification through 
artificial selection. Its history before the 
period of its domestication is unknown 
The best we can do is to point to the 
wild ancestor and say, “Here is where 
our particular variety had its origin.” 
Since the period of its cultivation, how- 
ever, the changes have been rapid and 
always in the direction best suited to 
the wants of mankind. We have studied 
the habits, adaptations, wants, likes and 
dislikes of fruits, and more especially the 
apple, because it is the “King of fruits,” 
and have reduced this study to more or 
less of a science. We have systems of 
experimentation and discovery which tend 
