A Bacterial Disease oe Alealfa 9 
soil carrying capacity of our winds, and with this in mind, it is 
easy to understand how germ laden soil might be blown into these 
cracks, where it would adhere to the moist, exposed surface, and 
bring about a fatal inoculation. As a matter of fact, soil was al¬ 
ways found adhering to these surfaces, and, already, typical cases of 
the disease were developing. A microscopic examination of the 
tissues from the injured areas usually showed the germs to be 
present in great numbers, while ten days previous, that is before the 
splitting had occurred, there was no indication of any infection. 
Invariably, the disease appeared first and was worst on those parts 
of the stem where the epidermis had split and where soil had been 
caught in the open wound. A striking example of this was seen in 
an alfalfa field adjacent to a field which had been cultivated re¬ 
cently and sown to oats. The oat field was on the windward side, 
and with every gust, quantities of fine soil were carried over into 
the alfalfa. All along this side of the field, there was an aggra¬ 
vated attack of the disease, extending twenty to thirty feet into the 
alfalfa and the whole length of the field. Every plant was gray 
with soil and it is only reasonable to suppose that the disease was 
more severe here than in the more remote parts of the field because 
of the heavier soil inoculation. 
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 inocula tion s in the 
* (l) Bulletin 138, Colo. Exp. Sta., Jan. 1909. 
