314 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
to attack is very short, since the tree passes rapidly into its summer 
state with its increased power of • resistance. When, however, the 
larch is planted in such a country as England, with a mild winter 
and a long and damp spring, the period of foliation extends over six 
or eight weeks, instead of two as in the Alps, so that insects and fungoid 
enemies have a much longer period during which to do damage. 
One of the great enemies of the larch is the fungus Dasyscypha 
Willkommii, which effects a lodgment in wounds in the young leaves 
and shoots made by plant-lice (Chermes laricis) or the mining-moth 
(Coleophora laricella), or by some other injury which breaks the surface 
continuity. In such a wound the spores find a favourable nidus, 
whence the mycelium penetrates into the cortex during the quiescent 
period of winter. 
If the tree has sufficient vitality it may succeed during the period 
of active growth in cicatrizing the canker-spot by surrounding the 
blister by a tough corky layer and thus arresting its progress. 
But under less fortunate conditions, when autumn returns, the 
mycelium penetrates further into the cambium and enlarges the 
canker-spot. Eventually it reaches the wood and interferes with 
the flow of sap. The further the invader advances the more is the 
resisting power of the host plant weakened, while such loss of resistance 
quickens the progress of the fungus. In course of time the tree 
sickens and dies. 
Bacterium Hyacinthi. — The yellow bacteriosis of hyacinth bulbs 
may serve as an example of a specific and fatal bacterial disease, 
being due to Bacterium Hyacinthi. Healthy bulbs are rarely attacked ; 
but if a wound or other condition has impaired vitality infection 
readily follows. The sequence may thus be represented : 
Growth of Bacteria > Breaking up of living cells 
In the early stage of bulb infection the disease is confined to the 
vascular bundles, from one to fifty of these being yellow and full of 
bacterial slime. But at a later state the disease spreads to the inter- 
vening parenchyma, and finally the whole bulb is destroyed. 
These examples of injurious circular reactions in phytopathology 
might be indefinitely multiplied. But they suffice to indicate the 
operation of a wide-spread principle. The process belongs to those 
fundamental biological phenomena which are common to both the 
higher animals and plants. Within the limits of health organization 
is of unquestioned advantage. But the liability to pernicious and 
reciprocal correlations is a serious penalty paid for such organization 
when physiological processes are disturbed by disease. 
Supply of Nutriment 
to Bacteria 
