REED: SPECIALIZATION OF PARASITIC FUNGI 389 



In some cases the parasite seems to be restricted to a single species, 

 for the fungus on Sisymhrium officinale does not infect 5. sophia. On 

 the other hand the same race occurs on Brassica oleracea and B. rapa. 



Taphrina aurea (Pers.) Fr. Giesenhagen (60), as a result of his 

 work on the Exoasceae, suggests that Taphrina aurea, which infects 

 three species of Populus, is becoming specialized into races, each of 

 which is adapted to a single species of Populus. 



Claviceps purpurea (Fr.) Tul. Stager (142) has found five special- 

 ized races in the ergot of rye, Claviceps purpurea. One race occurs on 

 rye and also on seventeen other species of grasses ; a second race occurs 

 only on Glyceria fluitans; a third is confined to species of Lolium; a 

 fourth to Pea annua; while the fifth is found on Brachypodium sil- 

 vaticum and Milium effusurru. Both conidia and ascospores, where 

 tested, are limited in the same fashion. 



Stager did not find any such specialization in Claviceps micro- 

 cephala. This ergot is reported on only three grasses. 



Plowrightia morbosa (Schw.) Sacc. Gilbert (61) reports that 

 Plowrightia morbosa (Schw.) Sacc. is specialized on the choke cherry 

 {Prunus virginiana) and wild plum {Primus americana). Ascospores, 

 conidia, and pycnospores from the former host were inoculated into 

 the wild plum without giving any evidence of infection. On the other 

 hand, ascospores and conidia under like conditions, readily infected 

 the choke cherry, giving rise to normal knots. A study of the distri- 

 bution of the fungus on the two hosts lends confirmatory evidence as 

 to the specialization, for in one locality the disease may be prevalent 

 on one host while absent from the other. 



Rhytisma acerinum (Pers.) Fr. Muller (104) has made a study of 

 this parasite on various maples and concludes that it consists of 

 several specialized races. One race Platanoides is found on Acer 

 platanoides infecting only slightly Acer campestris and A. pseudo- 

 platanus; a second race Campestris occurs on Acer campestris, to a 

 slight extent on A. platanoides, but does not occur on A. pseudoplata- 

 nus; a third race, which is given specific rank as Rhytisma pseudopla- 

 tani, occurs only on Acer pseiidoplatanus. Tubeuf (162) inoculated 

 Acer pseudoplatanus , A. platanoides, A. campestris and A. negundo 

 with ascospores from the first named host, infection occurring only 

 on this one maple. 



Colletotrichum lindemuthianum (Sacc. and Magn.) Briosi and 

 Cavara. Barrus (16) has studied the relation of bean varieties to the 

 common anthracnose, Colletotrichum lindemuthianum. He tested the 

 susceptibility of one hundred sixty-one varieties to a culture of this 

 organism and found that, while most of the varieties were susceptible 

 in varying degrees, a few seemed to be immune. When, however, 



