CONTRIBUTIONS FROM THE WISLEY LABORATORY, 487 



diseased plants in February (fig. 106, n). These were placed in water 

 at the bottom of a watch-glass, and the cells were capable of sending 

 out hyphae, although no conidia were observed under these conditions 

 (fig. 106, g). This type of growth is, of course, common in all groups 

 of fungi. 



Penetration of the Fungus. — The method of penetration of the 

 germ tube of the fungus was definitely determined by careful infection 

 experiments. Pieces of healthy leaves were painted over with water 

 in which germinating spores were suspended, and placed in a Petri 

 dish on steriHzed blotting-paper. After four days pieces of the leaves 

 were cut and imbedded in the usual way. Microtome sections cut 

 at a thickness of 5 /x showed the germ tubes boring through the epi- 

 dermis (fig. 107, a), and spreading themselves between the cells of the 

 tissue immediately underneath. The germ tubes were also observed 

 penetrating the leaf by way of the stomata (fig. 107, b). Under these 

 conditions of infection, spores were produced a little under three 

 weeks from the day of inoculation. 



Other Experiments. — The fungus Heterosporium gracile has been re- 

 corded on Narcissus, Gladiolus, and other monocotyledons. J. Ritzema 

 Bos, in describing Narcissus attacked by Heterosporium, remarks upon 

 the extraordinary rapidity with which the disease spreads. He regards 

 the fungus as a true parasite, but it can also live saprophytically in the 

 leaves which it has itself killed, and it is here, on the dead leaves, that 

 it forms spores. This leads him to hold that the fungus was first of 

 saprophytic nature. In years when the disease is not prevalent it 

 occurs on wounded overground portions of the plants. The Dutch 

 bulb-growers maintain that the withdrawal of the dead shrunken 

 remainder of the faded flowers is an excellent means of preventing the 

 disease, but the parts must be removed without injuring the still 

 living flower stalk. His examination of the faded flower parts showed 

 the presence of Heterosporium spores even before the fungus had 

 appeared on the hving leaves. 



It seemed desirable to endeavour to find whether the fungus from 

 diseased Iris would infect Narcissi. Narcissus plants were lifted from the 

 open ground in February and potted directly with much soil attached. 

 The plants suffered in no way from their removal, and were kept in the 

 greenhouse attached to the laboratory. At a later date the plants 

 were inoculated at the same time as the infection experiments with the 

 Irises, and spores were taken from the same cultures. Each pot was 

 placed on a flower-pot dish with a little water and then covered with a 

 beU glass. Other plants were kept as controls. The plants were under 

 daily observation, but no spots such as those which appeared on the Iris 

 leaves were seen. The leaves completed their growth, turned brown 

 at the tips, and withered away in a perfectly natural manner. Between 

 ten and eleven weeks after inoculation, black felt-like growths were 

 seen on the inoculated leaves, and were thought to be those of some 

 saprophytic mould, but on microscopic examination the spores and 

 hyphae of Heterosporium gracile were found to be present in abundance. 



