S. l^ Wiltshire 337 



These very artificial conditions were rendered necessary by the 

 peculiar and special conditions under which the fungus infects the 

 host and even under these, apparently the most favourable, infection 

 is by no means always successful. There must remain, therefore, some 

 slight possibility that the results obtained are simply pathological, but 

 since the growth of the mature mycelium in nature is in many ways 

 similar to that of the germ tube in infection, it is thought that this 

 possibility is not very great. 



Methods. Examination of inoculations was carried out by the 

 ordinary method of serial sections, the fixatives mostly employed being 

 chromacetic and acetic alcohol, with fuchsin and Licht Griin, and iron 

 haematoxylin as stains. The course of infection was also watched from 

 surface view from permanent preparations made as follows : inoculated 

 portions were fixed in acetic alcohol for about half an hour, then washed 

 and decolorised by absolute alcohol and finally mounted in Gilson's 

 mounting medium, which is not so refractive as Canada balsam. 



Germination. The conidia of V. inaequalis and V. pirina germinate 

 readily in water, most of them showing a germ tube of considerable 

 size after 24 hours, although some take a much longer time. The 

 conidia are easily wetted, and their specific gravity is so heavy (or 

 immediately becomes so on moistening) that on immersion in a drop 

 of water they almost immediately sink to the bottom of it, where 

 some change takes place, so that the conidium becomes attached to 

 the surface on which it is resting. The comparative difficulty with 

 which conidia about to germinate are washed from the slide on which 

 they have rested suggests a definite attacking envelope, but although 

 indications of an outer gelatinous layer have been seen under the 

 microscope they are in all probability optical illusions, for similar 

 indications are found with conidia of other fungi. In nature the 

 germinating spore must after a short time experience desiccation and 

 other changes due to the weather, but it is an extremely important 

 point with regard to the beginnings of infection, that notwithstanding 

 subsequent drying up germination can only be initiated after complete 

 immersion in water for some time — a fact originally discovered by 

 Aderhold, but perhaps hardly fully appreciated by the few more recent 

 workers. It seems indeed rather curious that in an atmosphere 

 saturated with aqueous vapour a spore will not germinate; and, as 

 will be seen later, the correct appreciation of tliis fact, which has been 

 repeatedly confirmed by the author, is of importance in understanding 

 some of the characteristics exhibited by these fungi. Immersion in 



