EVOLUTION OF PAKASITIC FUNGI. 108 



gists -whether the two fungi are riglitly separated into two 

 species. Cultural experiments will probably settle this question, 

 and there is some evidence of this kind which goes to show that 

 the two are distinct species. This is partly supported by the 

 discovery of what is supposed to be the perfect stages of these 

 fungi, since the form in which Ave knew^ them on the apple and 

 pear is what is called the " imperfect," or conidial stage. 



Brefeld cultivated a species of Venturia, which he called V. 

 ditricha j^lri, and from the ascospores he succeeded in developing 

 a conidial form which bore such a strong resemblance to the 

 FHsldadiuTn jnrinum, that he considered the Venturia to be the 

 perfect or ascosporous stage of the pear scab. Aderhold, in 

 1894, found another species of Venturia, V. chlorospora mali, on 

 apple leaves, from Avhich he grew a conidial form very nearly 

 like the Fushiadiuin dendviticum (the apple scab). Then he 

 recounts also how he was able, starting from the fungus of apple 

 scab taken from the leaves of the apple, to grow the conidial 

 stage in artificial media and also to develop the venturia stage, 

 which would be pretty good evidence that the venturia is the 

 perfect stage of the apple scab. AVe should also expect to find 

 that a venturia is the perfect stage of the pear scab, and this per- 

 fect form Aderhold hoped to find in the Ventiivia ditricha jiirl of 

 Brefeld. But in searching on pear leaves for this species of 

 Venturia he found both Venturia ditricha jw'i of the pear, and 

 also Venturia chlorosjjora mali of the apple, and this has pro- 

 longed the investigation. But if' the apple and pear scab should 

 be found to be one and the same species — and I do not anticipate 

 that this will be the case — still the parasitism would be quite 

 restricted in range as compared with the species above enu- 

 merated. It is quite in accordance with the theories of descent 

 that at least in the remote past a single species of Fusicladium 

 combined the characters of the now two species, or at least 

 possessed the inherent tendencies which have resulted in the 

 evolution of these two forms. 



Many of the species of the genus Se]eroti?ii<i exhibit well the 

 tendency to a narrow range in the parasitic habit, as the Sclero- 

 'tinia vaccina Wor., on Vacciniuui Vitis-IdcKa ; Sclerotinia Oxij- 

 cocci "Wor., on J^accinium Oxycoccus : Sclerotinia haccaruvi 

 Schroeter, on Vaccinium mi/rtillus : Sclerotinia megalosimra on 

 Vaccinium. idiginosum ; and others. On the other hand, one 



