JEHANGIR FARDtJNJI DASTUR. 183 



were used for inoculating healthy leaves. When the fungus was 

 taken in culture, zoospores suspended either in distilled water or in 

 sterilised tap water were invariably used for the various inocula- 

 tions. Whatever was the technique employed for the inoculation 

 the result was always the same. The effect of the inoculation 

 was clearly perceptible within twenty-four hours by the inoculated 

 area taking a dull unhealthy green colour. Sporangia were 

 produced in about forty-eight hours after inoculation, when the 

 inoculated leaf was kept moist by occasionally spraying it with 

 water. The inoculated leaves could be easily induced to produce 

 sporangia by suspending them in tap water. They readily dis- 

 charged their zoospores when transferred to a drop of fresh water. 

 These zoospores were used to inoculate a new set of leaves of 

 healthy plants. The inoculation took as readily as in the previous 

 experiments. In the case of leaves of tender seedlings and of very 

 young leaves of bigger plants the disease spread from the lamina 

 to the petiole, thence to the stem. 



From these infection experiments it is found that the germ- 

 tubes of the zoospores penetrate the leaf three to five hours after they 

 are sown on it. The penetration takes place on either of the sur- 

 faces and is not accomplished necessarily through a stoma. They 

 may even break through the upper wall of the epidermal cells or 

 penetrate between the cell walls of two neighbouring cells (Plate 

 III, Figs. 5-11). What factor stimulates the germ- tube to enter the 

 host plant in one way or the other is difficult to say ; very often it 

 has been found to cross over a stoma without entering it (Plate 

 III, Fig. 10). Before the germ-tube enters the leaf its end is slightly 

 enlarged as a rule. 



We have seen that in nature the fungus is confined to seedlings 

 and to leaves of older plants. Stems of tender seedlings about six 

 to eight inches high are found diseased in nature. When a stem of 

 a healthy tender seedling is inoculated by means of zoospores sus- 

 pended in a drop of water, the inoculated area soon turns brown. 

 The disease extends in both directions, ultimately reaches the 



