241 



Whether the neck of the pycnidiiim is glabrous or 

 hirsute is generally considered an important systematic 

 character; according as the fructification is hairy or not, 

 the fungus is placed in the genus Chaetodiplodia or Diplo- 

 dia. Our culture experiments showed, however, that this 

 character is whoUy governed by external conditions. 



Fruits, which had been successively treated with aO,o% 

 solution of corrosive sublimate, washed with stérile water 

 and infected through a little wound with Chaetodiplodia 

 spores, were placed under a glass bell-jar. The fruits gave 

 off enough moisture to cause dew formation on the jar 

 and to keep the air moist during the experiment. Generally 

 the pericarp began to turn brown round the wound after 

 two or three days; the discoloration spread rapidly and 

 after a few days the grey woolly pycnidia with a hairy 

 neck made their appearance. The fruit had then the appea- 

 rance illustrated in Fig. 3 and microscopical préparations 

 resembled Fig. 8. 



If the fruits are treated in the same manner, but if, 

 after infection or after the appearance of the brown 

 coloration, they are not kept in a closed space, but are 

 laid down or hung up in the laboratory, the pycnidia do 

 not make their appearance. A large number of small 

 openings are indeed formed in the pericarp, and from 

 ^hese long, white and often strongly curled tendrils pro- 

 trude. On microscopical examination thèse are seen to 

 be the unripe colourless spores, which are extruded from 

 the opening of the pycnidium and remain connected for 

 some time as threads. They gradually become grey and 

 then black. In this case the pycnidia themselves do not 

 protrude so far from the pericarp. The fruit then resembles 

 the one of Fig. 4. Often the neck of the pycnidium is 

 quite glabrous as in Fig. 9. Sometimes it has a few 

 hairs, but there are never enough to be recognized by 



