858 
Journal of Agricultural Research 
Vol. XXXI, No. 9 
tomato ( 5j p. 148) a correlation was found between the resistance of 
ripe fruit to infection and the higher hydrogen-ion concentration in 
the ripe fruit as compared with the leaves and green fruit, and in that 
disease also the younger parts of the plant were more susceptible to 
infection. 
Clevenger (4, p. 238) found that the hydrogen-ion concentration 
of cowpea leaves was slightly lower than in the stems, and that it 
showed a diurnal variation (4, p. 233). A maximum concentration 
(P H 5.27) occurred in the leaves at 10.30 a. m. and a minimum 
(P H 5.81) at 1 a. m., while in the stems a maximum (P H 5.04) occurred 
at 6.30 a. m. and a minimum (P H 5.32) at 9 p. m. The writers in 
their cultural tests found that the parasite tolerated a P H of 4.5 
and grew well at P H 5.00, so it is evident that the cowpea leaves 
and stems are well within the limit of tolerance. The lower acidity 
of the leaves in the night may favor infection at that time. 
Atomizer inoculation has been successful upon all of the varieties 
of cowpea, sieva bean, and lima bean tested, including most of the 
varieties mentioned in the previous discussion of hosts of this disease, 
and upon the catjang, hyacinth bean, adsuki bean, and Florida velvet 
bean (varieties, Bunch and 100-Day). The organism was successfully 
reisolated from each host species. The three Phaseolus limensis 
varieties—Burpee, Fordhook, and Large White Pole—have appeared 
to be more susceptible than Hendersoms Bush Lima, which, according 
to Bailey (1 , p. 396) , is a different species. In fact, in the writers 7 
field plots in 1924, Henderson’s Bush Lima showed considerable 
resistance. Wliile the cowpea varieties have been considered equally 
susceptible, the varieties Early Red, Clay, California Blackeye, Iron, 
Groit, and Whippoorwill were more severely diseased than any of the 
other 12 varieties in the 1923 plots. In the 1924 plots the varieties 
Early Red, Groit, WThippoorwill, New Era, and Catjang were more 
- severely diseased than Blackeye, Iron, and Early Buff. Rather 
light natural infection occurred on the foliage of velvet beans grown 
adjacent to cowpeas in 1924, and the-organism isolated resembled 
Bacterium vignae in culture, and in inoculation tests produced typical 
lesions on cowpeas. 
The organism isolated from the lesions on Desmodium canescens 
resembled the cowpea organism in culture, and in cross-inoculation 
tests in a field cage and in the greenhouse produced typical bacterial 
spot infection on cowpeas. The organism was successfully reisolated, 
and although its morphology and cultural characters have not yet 
been studied by the writers, it seems safe to assume that the Desmo¬ 
dium organism is Bacterium vignae. The importance of this weed 
as a possible source of infection is not known. 
Unsuccessful attempts have been made to inoculate garden beans 
(five varieties), soy beans (five varieties), broad bean, sweet pea, 
peas (seven varieties), lupine, clovers (white, Bokhara, crimson, 
annual sweet, mammoth red, and alsike), cauliflower, tobacco, 
tomato, and potato. 
RELATION OF PARASITE TO HOST TISSUE 
As atomizer inoculation of cowpeas without wounds is successful, 
it seems likely that the tissues are entered by way of the stomata. 
Tisdale and Williamson (24, P• 1&1) found that the lima-bean leaf 
was invaded through .the stomata. Microscopic examination of the 
