488 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



The control plants behaved in exactly the same way, with regard to 

 their length of growth and withering of the leaves, but in no instance 

 were the spores of Heterosporium gracile found. 



Infection experiments were also performed with leaves placed in 

 Petri dishes in the manner described above, in the case of Iris, and in 

 these experiments spores were formed only after the leaf was dead. 

 The method of inoculation was repeated a number of times with the 

 same results. 



Close observations were carried out with regard to the Narcissus 

 plants in the gardens, of which there is a large and representative 

 collection, but in no instance was a plant found with Heterosporium 

 gracile growing upon it, either on the living or on the dead foliage. 

 Mr. Chittenden also searched his garden, where some Irises are 

 attacked by Heterosporium gracile, but he was unable to find a 

 Narcissus plant affected. 



Experiments were conducted for the purpose of infecting Gladiolus 

 and HemerocaUis leaves, but without success, the leaves becoming 

 covered with saprophytic moulds before the Heterosporium had 

 completed its Hfe cycle. 



Vitality of the Spores. — The time during which spores would retain 

 their vitality was considered with a view to ascertain if these 

 were the means of starting the outbreak the following year. No 

 difficulty was experienced in collecting spores from diseased leaves 

 from October until the end of January, and these were germinated 

 in watch-glasses or hanging drops, according to the number of spores 

 that were found. Sharp frosts were recorded at Wisley in January, 

 and on the 23rd of this month the temperature on the grass was 8°F. 

 On the afternoon of this day spores which had been exposed to the 

 frost were placed in water and left until the 26th, by which time nearly 

 every one had germinated. Spores were much scarcer by the beginning 

 of February, but could be germinated in hanging drops. The gathering 

 and germination of spores were continued until March 29, after which 

 date no spores could be found ; in every case the spores were capable 

 of germination. Sharp frosts were recorded from January to March, 

 and it is therefore apparent that the spores are capable of resisting a 

 temperature much below freezing-point. This, in a thick-walled spore, 

 is not surprising. Fungi are known to retain their vitaHty even if sub- 

 jected to the lowest temperature at present obtainable, as is pointed 

 out for example by Buller and Cameron in the case of Schizophyllum 

 commune* 



It is probable that the spores of the fungus are distributed by means 

 of wind and rain from one leaf to another during the summer and winter, 

 or they may fall to the ground, where they remain in a resting state, 

 ready to start the disease in the spring and summer. 



The thick-walled masses of hyphae observed in the diseased leaves 

 in February which were capable of sending forth hyphas are also a 

 means by which the fungus may be continued from one season to the 

 * Trans. Brit. Mycol. Society, iv. (1913), p. 106. 



