masses into which the mature "plant"
condenses.

B. The bacterium with and without its gelatinous sheaths (cf. fig. 19).

C. Typical filaments and rodlets in the slimy sheaths.

D. Stages of growth of a sheathed filament--a at 9 A.M., b at 3 P.M., c at
9 P.M., d at 11 A.M. next day, e at 3 P.M., f at 9 P.M., g at 10.30 A.M.
next day, h at 24 hours later. (H. M. W.)]

[Sidenote: Bacteriosis in plants.]

Bacterial diseases in the higher plants have been described, but the
subject requires careful treatment, since several points suggest doubts as
to the organism described being the cause of the disease referred to their
agency. Until recently it was urged that the acid contents of plants
explained their immunity from bacterial diseases, but it is now known that
many bacteria can flourish in acid media. Another objection was that even
if bacteria obtained access through the stomata, they could not penetrate
the cell-walls bounding the intercellular spaces, but certain anaerobic
forms are known to ferment cellulose, and others possess the power of
penetrating the cell-walls of living cells, as the bacteria of Leguminosae
first described by Marshall Ward in 1887, and confirmed by Miss Dawson in
1898. On the other hand a long list of plant-diseases has been of late
years attributed to bacterial action. Some, _e.g._ the Sereh disease of the
sugar-cane, the slime fluxes of oaks and other trees, are not only very
doubtful cases, in which other organisms such as yeasts and fungi play
their parts, but it may be regarded as extremely improbable that the
bacteria are the primary agents at all; they are doubtless saprophytic
forms which have gained access to rotting tissues injured by other agents.
Saprophytic bacteria can readily make their way down the dead hypha of an
invading fungus, or into the punctures made by insects, and Aphides have
been credited with the bacterial infection of carnations, though more
recent researches by Woods go to show the correctness of his conclusion
that Aphides alone are responsible for the carnation disease. On the other
hand, recent investigation has brought to light cases in which bacteria are
certainly the primary agents in diseases of plants. The principal features
are the stoppage of the vessels and consequent wilting of the shoots; as a
rule the cut vessels on transverse sections of the shoots appear brown and
choked with a dark yellowish slime in which bacteria may be detected,
_e.g._ cab