106 Brown. — -Studies in the Physiology of Parasitism. VIII. 
by the petal becoming limp and flaccid and by the discharge of the colour. 
Microscopically it is shown by the failure of the cells to undergo plasmolysis 
in hypertonic solutions. In no case were results taken from petals which 
showed any discolorations due either to the accidental presence of fungal 
contamination or to the general ageing of the petals. Numerous tests were 
made on the petals at the end of each experiment to see if any diminished 
capacity for plasmolysis could be demonstrated. In this way it was shown 
that petals which had been under treatment for several days still possessed,, 
as far as could be seen, a edacity of undergoing plasmolysis equal to that 
of fresh ones. In both cases, after immersion of the petals in molar 
potassium nitrate, a very large percentage of distinctly plasmolysed cells, 
i. e. with sharply marked contracted highly coloured vacuoles, is seen, 
together with a small percentage in which the evidence of plasmolysis is 
not so distinct. Numerous tests led to the conclusion that the treated and 
the fresh petals were indistinguishable in their plasmolytic features. It was 
frequently found that the experimental petals showed after several days’ 
treatment a characteristic mottling due to the presence of numerous small 
translucent patches. Examination of the latter showed that they were due 
to injection of the intercellular spaces with liquid. The distribution of 
these injected patches showed no relation to the position that had been 
occupied by water-drops, whence it follows that the liquid was derived from, 
the cells themselves. Such self-injected petals invariably gave high 
conductivity figures. Nevertheless, on immersion in molar potassium 
nitrate they showed a degree of plasmolysis indistinguishable from that of 
fresh petals. 
Germination Studies. 
■ 
The conductivity method was largely used on account of its ease and 
simplicity, but, as was pointed out above, the real criterion of the importance 
of exosmosis in the physiological processes of infection is the effect of the 
fluid of the experimental drops on fungal germination. Germination 
studies, carried out as already described, showed that a high conductivity 
figure was associated with high germinative capacity and vice versa. The 
degree of correspondence observed will be seen in the following table, which 
embodies the results obtained in an experiment specially set up for this 
purpose. 
In this experiment petals were obtained from an unopened bud of 
Cereus. They were thus free from fungal contamination or other blemish. 
In order to obtain a wide range of conductivity figures, the water drops 
were allowed to remain in contact with the petals for different lengths 
of time. 
