254 Journal of Agricultural Research voi. xxiv, no. j 
cases of natural infection. When suitable for inoculation they were 
removed to another greenhouse where the inoculations were performed. 
In practically every case equal numbers of plants were inoculated with 
nonvirulent juice as controls. Insect-transmission experiments were 
conducted in cages in a third greenhouse with plant material raised in 
the greenhouse first mentioned. In these experiments also equal num¬ 
bers of control plants were placed in adjoining cages. No case of mosaic 
has occurred among the control plants in any experiment performed. 
In some experiments a method of handling aphids was developed by 
which the tedious operation of lifting individual insects with a camel’s 
hair brush was eliminated. Small bits of infected sorghum leaves 
covered with the insects were clipped off with scissors and placed on or 
tied to the plants to be tested. Similar pieces of leaves from which the 
insects had been carefully r^noved were tied to a series of control plants^ 
and healthy leaves with nonvirulent aphids were tied to a second series 
of control plants. Although it is necessary to run two sets of control 
plants in order to check all factors properly, this method was found to 
be of great convenience. The experiments noted in Table III were 
performed in the manner described. 
TablB III .—Results of a test of the insect transmission of grass mosaic by the neur 
method. 
Species. 
Num¬ 
ber of 
plants. 
Date exposed. 
Treatment. 
Resi 
Date 
examined. 
ults. 
Condition. 
Sacchafum offi^marum 
3 
Aug. 3,1920.. 
Aphids on mosaic leaf..... 
Aug. 34, 1920. 
2 mosaic. 
var. Ipuisiana Purple 
3 
.do. 
Mosaic leaf, no insects. 
Sept. IS, 1920. 
All healthy. 
l>o....... 
3 
.do. 
Aphids on healthy leaf.... 
.do. 
Do. 
Zea mays.. . 
3 
.....do. 
Aphids on mosaic leaf. 
Aug. 30, 1920. 
2 mosaic. 
Do.... 
3 
.do. 
Mosaic leaf, no insects. 
Sept. IS, 1920. 
All healthy. 
Do..*.. 
3 
.do. 
Aphids on healthy leaf.... 
.do. 
Do. 
Holcus sorghtsm . 
3 
.... .do. 
Aphids on mosaic leaf. 
Aug. 26, 1920. 
Both mosaic. 
Do..... 
2 
.do. 
Mosaic leaf, no insects. 
Sept. 15, 1920. 
Both healthy. 
Do.. 
2 
.do. 
Aphids on healthy leaf.... 
Do. 
Miscanihus sintnsis. .. 
i 
.. ..do. 
Aphids on mosaic leaf. 
Aug. 30, 1920. 
Mosaic. 
Do....... 
I 
.do. 
Mosaic leaf, no insects. 
Sept. 15, X920. 
Healthy. 
Do,,.. . . 
I 
.... .do___ 
Aphids on healthy leaf.... 
.do. 
Do. 
Syniheristna sanguhia- 
7«c 
, 2 
.do. 
Aphids on mosaic leaf. 
Aug. 30, 1920. 
Both mosaic. 
Its* 
Do. 
2 
.do. 
Mosaic leaf, no insects. 
Sept. is» 1920. 
Both healthy. 
Do.,.. 
2 
.do........ 
Aphids on healthy leaf.... 
.do. 
Do. 
Although a considerable number of species of insects have been tested 
for their ability to act as carriers of grass mosaic, it has been demonstrated 
ovly iox Aphis maidis {A. adusia) by the writers. Our results on the 
transmission of the disease with this insect have been corroborated by 
Ledeboer (ij) who has also succeeded in transmitting it by the use of 
A. sdcchari. Owing to its abundance and omnivorous habits, A. maidis 
has hetn found very convenient for use in ascertaining the susceptibility 
to mosaic of various grasses. Several grasses, notably corn and millet, 
havfe he^h found by the writers to be very difficult or even impossible to 
infect by artificial inoculation, but it is comparatively easy to bring about 
infection* by the use 6f virulent corn aphids. The corn aphids, of course, 
dh not feed on all the grasses equally well, and on some it was found quite 
impossible to establish them. They are not abundant on sugar cane. 
^ Since tbi$,paper wds prepared, nearly two year^. ago, the work reported in ledeboer's pfeliminary 
report Has atipeared: WitsRiNK, G. oNDERioeK naar P® vERBRErbiNo per GEtBstREPEN- 
ziEKTE DOOR BLADtuizEN. ” In Archief Suikerindus. Nederl.-lndie, Meded. v. h. proefst. y. d. 
Javasuikerindus. 1922, no. lo, p. 413-456. Dr. Wilbrink confirms A. as a vector of mosaic but 
not A. sacchari. 
