800 The American Naturalist. [October, 
young bulbs are cut, the plateau (central short stem of the 
bulb) is often found to be the only diseased part, something 
inexplicable if we do not admit that the disease has been 
transmitted to the bulblet from the mother bulb. Such isthe 
usual form of the disease, but it will be understood that there 
are numerons modifying circumstances, the disease sometimes 
beginning lower down on the edge of the leaf, or even under- 
ground, or progressing more rapidly, the latter especially 
when the disease attacks full grown leaves and scapes. The 
most cases of the first stage of the disease are noticed in the 
field in May, but cases also occur much earlier in the year. 
(4) Pathological Histology—tIn spring, in the first stage of the 
disease, when only the tips of the leaves are attacked, micro- 
scopic examination shows the bacterial slime to be present in 
the intercellular spaces of the shrivelling leaf-parenchyma, but 
always only in small quantity. From this part of the leaf the 
bacteria may be traced long distances down the vascular 
_ bundles, but have not yet reached the bulbs, the latter being 
still entirely sound. Inautumn, on the contrary, cross sections 
of the bulbs, if not too badly diseased, show numerous yellow 
dots in the scales, and on microscopic examination these are 
found to correspond to the xylem part of the vascular bundles 
(No. 34, pl. I, figs. 9, 10). The vessels of the latter are seen 
to be full of a thick, yellow slime, which often partially 
dissolves them. Here and there, the whole xylem part of the 
bundle may disappear, the yellow slime taking its place. In 
this way are formed continuous, tubular cavities, filled with 
isolated cells of the host plant, remnants of spiral threads, and 
an innumerable number of bacteria. In this stage of the dis- 
ease, the sieve tubes are not yet attacked, but these are subse- 
quently destroyed, and frequently, also, the parenchymatic 
tissues outside of the bundles, the substance which unites the 
cells being first dissolved. The second spring, a microscopic 
examination of the yellow striped leaves from diseased bulbs 
shows a similar occupation of the vessels with the same 
lesions, but in a reverse order, the bacteria being most abund- 
ant and the destruction of tissues greatest in the basal part of 
the leaf. Here the bacteria dissolve the walls of the vessels 
