A Bacterial Disease oe Alfalfa i i 
This explanation satisfies one of the most difficult questions 
which has arisen in connection with the problem, namely, why does 
the first cutting, alone, suffer from the attack? There are never 
any frosts after the first crop is out of the way, and consequently 
there are no split stems in which to start the infection. 
In a preliminary report (i), the writer has suggested that pos ¬ 
sibly the constant tramping of cattle and horses, pastured on the 
alfalfa fields during the winter, might have split open the crowns 
and bruised the young, tender shoots so that during the first irriga¬ 
tion, soil containing the disease germs was washed into the injured 
tissue and started the trouble on the first cutting. Our observations 
during the past season do not warrant such a conclusion in the 
majority of cases at least, since, in the first place, the disease was 
active at least two weeks before the first irrigation, and in the 
second place, our experimental plats, to which stock had no access, 
suffered just as severely as the fields which were pastured. 
Not infrequently, we find the disease at work on stems where 
there has been no apparent previous injury to the epidermis; some¬ 
times this assumes the form of a continuous, unbroken infection of 
the whole internode, and again it occurs as separate, punctiform 
lesions giving the stem a speckled appearance. This last condition 
would seem to indicate an infection through the stomata, and in¬ 
asmuch as we have been able to secure successful inoculations in the 
greenhouse by applying the culture to the unbroken epidermis, it is 
altogether possible that stomatal infections take place under field 
conditions. The leaflets often exhibit yellowish, watery areas along 
the margin and the larger veins when there is no evidence of the 
trouble in any other part of the plant; again, the tiny petioles suc¬ 
cumb to the disease independently of either the stem or the attached 
leaflets. Water pore and stomatal infection similar to that des¬ 
cribed for the black rot of cabbage may explain these cases. 
There are doubtless other ways in which infection can take 
place, but the methods described above, especially the inoculation 
through the split epidermis, seem to be the most common. It is 
possible that added observations of another season will give us more 
light upon this point and so rather than draw any final conclusion 
as to the one way in which inoculation takes place in the field, we 
prefer to leave the question open. 
DESCRIPTION OE THE CAUSAE ORGANISM. 
Pseudomonas medicaginis, n. sp. (Sackett.) 
I. MORPHOLOGY 
1. Vegetative Cells. 
When grown upon nutrient agar for 24 hours at 28° C., and 
(1) Bulletin 138, Colo. Exp. Sta., Jan. 1909. 
