Ward, — Recent Researches on the Parasitism of Fungi . 41 
linked up to potash-bulbs. The other two were arranged in an exactly 
similar manner, except that their tower-tubes were not connected with 
potash-bulbs, and the air passing over their contained leaves passed through 
distilled water only. Clamps at various points enabled me to regulate the 
rate of ingress of air. 
All six tower-tubes containing leaves were now joined up to a central 
large flask, by means of tubes linked together, and the flask communicated 
with a vacuum-pump. On joining up the system, and starting the pump, 
a little regulation of the clamps easily enabled me to set up a current 
of air through the towers at uniform rate, and at a low pressure, viz. 
20-50 mm. of mercury— and this was done so that about one bubble per 
second escaped from the afferent tubes and passed over the leaf above. 
The histological examination of these infected leaves showed that as 
soon as the leaf feels the deprivation of carbon supplies the Fungus-hyphae 
begin to degenerate and starve ; and in some of the cases we find corrosions 
of the tissues beneath the spores on the epidermis. We have made out 
numerous interesting details regarding the degeneration of the nuclei, 
breaking up of the chlorophyll-corpuscles, thinning of the cell-walls, and 
so forth ; but since there is still much to be done before all the facts 
can be linked together I do not propose to go further into the matter 
here. 
The case of the plants with roots kept at high temperatures also 
promises to be interesting in several directions. 
I pointed out some time ago ( 190 , p. 291) that infections are difficult 
to carry out in hot weather, and gave evidence which goes to show that the 
mycelium suffers when the temperatures inside the leaf pass beyond certain 
limits. I also gave some experimental data showing that the temperatures 
in grass leaves exposed to a summer sun may rise far higher than is usually 
supposed. 
It is interesting to note that Dr. Blackman, working in our laboratory 
at assimilation and respiration, and using thermo-electric measurements 
and methods of greater accuracy than were at my disposal, has confirmed 
and extended these data ; as he will himself bring the matter before you in 
detail, I need say no more now. 
These failures of infection in hot weather are so common — we have 
experienced them several times this summer — and the phenomena are so 
similar to what occurs in our heated plants, that I am disposed to urge that 
both cases stand in the same category. 
But that is not all. The phenomena — starvation of hyphae in a nest 
of dead cells, or the corrosion of cells beneath the spores sown on the leaf — 
are similar in all these cases to what occurs on the so-called immune plants 
we have dealt with . 
