REED: SPECIALIZATION OF PARASITIC FUNGI 389 
In some cases the parasite seems to be restricted to a single species, 
for the fungus on Sisymbrium officinale does not infect S. 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 Poa annua; while the fifth is found on Brachypodium sil- 
vaticum and Milium effusum. Both conidia and ascospores, where 
tested, are limited in the same fashion. 
Stager did not find any such specialization in Claviceps mucro- 
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 (Prunus 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. Miiller (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 pseudoplatanus. 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, 
