the Economic Products of India.
Diseases of the Poppy Plant.
5
PAPAVER
somniferum.
CULTIVATION
Diseases.
Peronospora.
woven by a sterile mycelium, the decay of which caused their discoloration
and death. Again, the fungal discolorations and disease of the leaves
were communicated to the nodes,—i. e., the points of union of the leaf and
t h e
t h e s t e m , — t h e n c e e x t e n d i n g u p w a r d s a n d d o w n w a r d s f r o m e a c h a s a
centre, until the whole stem not unfrequently assumed a nearly uniform
glaucous bluish-black. At this stage all subsequent growth was arrested,
and the plant sooner or later died. The cuticle, or skin of the stem, was
seen to shrink and dry, but, unlike that of mould-affected potato-stalks, it
continued firmly adherent to the dry woody layers beneath. This close
adhesion of the epidermal layers to the woody zone tends, as I think, to
show that neither the cambium layer nor liber, or inner bark, has been
actually invaded by the mould; otherwise one might have expected a
separation of the epidermal or upper layers on the death of the mycelium
and softer tissues investing the wood. . . . The pith of plants affected
with mould acquires a brownish green colour, and in the earlier stages of
the disease becomes gorged with sap. As this is exhausted –apparently
in the supply of the capsules, which frequently continue green and soft,
and even mature their seeds after the leaves of the plants are dry and
withered—the pith also dries up, and the whole plant dies. . . . The
weather during the period of this mould-invasion was upon the whole dry,
with only light, occasional showers of rain. I do not doubt that with cold,
foggy, or rainy weather those mould-blighted plants would have become
so surcharged with sap, that all their parts would have become soft, and
instead of withering and drying as they did, would have become a pulpy,
rotten mass. This I now strongly suspect has been the case in the poppy
blight of 1871-72, as it appears to have been everywhere preceded by cold,
foggy, and rainy weather. It thus appears that, under certain unknown
conditions, there may occur either a merely vegetative extension of the
spawn or mycelium
in the tissues of the poppy leaves, or, on the other
hand, vegetative development may be in abeyance, and the reproductive
correspondingly exalted, to the complete exhaustion of the mycelial
processes. Now, in the latter case, we have a compara ively
h a r m l e s s
p a r a s i t i s m ,
the injury to the tissues of the foster parent being local,
and limited to those in immediate contact with the mycelium ; whereas
in the other case, with the reproductive function in abeyance, and a
purely vegetative development in force, the results are most mischievous :
this, as it appears to me, is due to the decay of the u nexhausted mycelium
in the tissues of its nurse. In all circumstances the spawn is but short
lived, decay fast following development ; and it is thus that the soft, almost
sebaceous tissues of the mycelium, full as they are of protoplasmic matter
and juices, cause alterations in the cellulose and cell contents of the sur-
rounding tissues, and generate a quasi -fermentive process, which being
communicated to the surrounding tissues, the whole organ, or indeed the
entire plant, undergoes decay. Now, it is easy to see that if this should
occur in cold, wet, and cloudy weather, when transpiration is checked,
and the tissues consequently less or more gorged with juices, the plant
will present all the symptomatic appearances of moist
g a n g r e n e ; t h e
leaves becoming soft, flaccid, and drooping with the first break of the
sun, while the softer tissues of the stem will speedily rot. In a dry and
hot atmosphere, on the other hand, while transpiration is increased and
the absorption of moisture from the soil impeded, by the decay of the
mould in the tissues, and the functional derangements thereby occasioned,
the fluid contents of the cells being nearly exhausted, the several parts of
the plant, as might be anticipated, do simply wither and die. Thus in the
first instance, we have one of those virulent rot-blights which ruined the
poppy-crops in 1871-72; and in the second it assumes the dry and less