78 



corroded edge an almost imperceptible fringe can be thus made out 

 by careful examination. 



Under a magnification of one hundred diameters this fringe is seen 

 to be composed of the aerial fruiting filaments of a fungus, very 

 much resembling that figured in the Agricultural Gazette, vol. Ill, 

 p. 289, as associated with a shot-hole disease of the apricot. 



This fungus appears to gain its entrance to the leaf at the points of 

 the marginal teeth. Every stage of its progress can easily be traced, 

 and the whole matter is most interesting. From the corroded tooth-point 

 to the gap whence half a lobe has disappeared, not a stage is wanting. 

 A water culture of this fungus was made as follows : A small piece 

 from the edge of a diseased leaf was cut away and placed under a 

 cover-glass, with just enough water to moisten it. The water applied 

 for this purpose, of course, as usual, washed away the spores from the 

 projecting hyphae, and they were left bare. These loosened spores 

 were sketched and resembled those shown in Fig. 89. The cover- 

 glass was then sealed on, and the fungus left to develop in the moist 

 chamber thus provided. 



After fifteen hours the edge of the piece of leaf presented a vastly 

 different appearance. Aerial hyphse had shot up and produced a 

 copious crop of spores, as represented in Fig. 89. These spores were 



borne only on hyphse growing in air. My- 

 celium in contact with the glass, and there- 

 fore in contact with water by means of 

 capillary attraction, did not produce these 

 spores. After twenty-four hours, jarring 

 the moist chamber would cause these aerial 

 spores to fall off, sometimes in clusters. 

 This gives us the time required for these spores to develop and ripen ; 

 and the speed with which it is done explains 

 clearly the ability of the fungus to corrode and 

 completely destroy a large fraction of a passion- 

 vine leaf in a few weeks. 



The spores spoken of as falling away on the 

 application of water were kept under observa- 

 tion, and were found to germinate in two differ- 

 ent ways, according as they were in water or 

 air. Those in water grew, 

 as shown in Fig. 90, while 

 those in the air produced a 

 crop of spores, as shown in 

 Fig. 88. Both these latter 

 sketches were made when 

 the growth was twenty- 

 four hours old. As will be 



seen from the adjacent measurements, the spores 

 of this fungus, which bears the closest resemb- 

 lance to that found and recorded by me on the 

 edges of shot-holes of the almond and the apricot, range in size from 

 4-6 x 9-16/x., and average 5'7 x 12'6/x. 



X400 



Fig. 88.-Germi- 

 nation in air of 

 a spore of the 

 oospora-like fun- 

 gus connected 

 with the faulty 

 leaves of the 

 passion-vine. 



15-8 x 6'3 n *) 

 13-0 x 6-3 

 9-1 x 4-2 

 12-6 x 6-3 

 13-3 x 4-9 

 12-6 x 5-6 

 11-2 x 5-3 

 12-6 x 5-3 

 12-3 x 67 

 10-9 x 6-3 

 14-0 x 5-6 

 14-0 x 5-3 



i Average, 



i f;r 



Fig. 89. Oospora-like fun- 

 gus connected with the 

 faulty leaves of the 

 passion- vine. 



