JEHANGIR FARDUNJI DASTUR. 185 



not far to seek. The tender stem of a seedling has an uncuticular- 

 ised epidermis, the outer wall of which readily permits the hyphre 

 to penetrate it, the cortex is soft and juicy and therefore easily 

 succumbs to the ravages of the parasite ; its growth is not entirely 

 checked on reaching the vascular bundles which, as we have seen 

 are attacked through the unthickened portions of their vessels. 

 On the other hand, the stem of an older plant presents obstacles in 

 its way from the very beginning. The outer wall of the epidermis 

 is highly cuticularised and so wards off an attack of the hyphse and 

 even if they get into the stem through stoma ta, the germinating tube 

 cannot go further on account of the thick-walled and closely packed 

 collenchymatous cells of the cortex. Apart from these reasons of 

 physico-chemical importance there may be very possibly others of 

 physiological importance. Colour is lent to this by the disease 

 confining itself to the lamina of a mature leaf of young plants and not 

 spreading to the petiole and thence to the stem. I have succeeded 

 up to now in inoculating petioles of only very young leaves. The 

 inoculation was made by placing distilled water containing motile 

 zoospores in a cup of moulding wax (Plasticine) which surrounded 

 a part of the petiole at the node and parts of the internodes above 

 and below it. The stem did not take the inoculation but the 

 petiole did, in two days. The stem was then attacked through the 

 latter. The hyphse which entered from the petiole extended up the 

 stem and killed the growing point. The growth of fungus in the 

 opposite direction was very slow. In these various experiments 

 it was found that not only under field conditions is the leaf bud 

 safe from the attack of the parasite, but also when inoculated 

 aritificially, on account of the sheathing stipules. 



Infection experiments have also been carried out on flowers 

 and fruits. For these experiments as well the inoculation material 

 was zoospores from pure cultures, suspended in either distilled or tap 

 water. Stalks bearing flowers and fruits were stood in water in 

 flower vases ; drops of water containing motile zoospores were placed 

 on the flowers and fruits. After the inoculation the flower vases were 

 kept in moist chambers. Stalks of flower and fruits kept as ' ' checks " 



