392 BROOKLYN BOTANIC GARDEN MEMOIRS 
Glyceria, Agropyron and Bromus; most of the races of P. glumarum 
and P. dispersa. 
3. Specialized races occurring on two or more genera but belonging 
to the same family. As examples, we may mention the specialized 
races Avenae, Secalis and Tritict of Puccinia graminis: Loli, Calama- 
grostis and Phalaridis of P. coronata; Secalis of P. glumarum; Orchide- 
arum-phalaridis of P. sessilis; the races of P. Ribesii-Caricis, P. 
extensicola, P. silvatica, P. Bistortae, P. mammullata, Albugo candida 
and Claviceps purpurea. 
4. Races occurring on hosts belonging to different families as 
Puccinia subnitens, Uromyces Scirpi and Erystphe cichoracearum. 
When we compare the specialization of a parasite in relation to a 
particular host we also find the greatest differences. For example 
Puccinia gramints avenae occurs, according to Eriksson (41), on twenty 
species of grasses belonging to fourteen genera, Carleton (25) recording 
it on nineteen species belonging to fifteen genera, Jaczewski (68) on 
seven species belonging to six genera and Stakman and Piemeisel (149) 
on thirty-three species belonging to twenty-one genera. All agree 
that this rust occurs on a wide range of more or less unrelated hosts. 
On the other hand, Puccinia coronata avenae is restricted to species 
of Avena and possibly Arrhenatherum. The powdery mildew of oats, 
Erysiphe gramints avenae, is also sharply restricted to Avena, infecting 
to some extent Arrhenatherum. The crown rust and powdery mildew 
are similar in infecting a large number of species and varieties of 
Avena. 
A similar condition is found in the case of the parasites occurring 
on Secale cereale: Claviceps purpurea secalis occurs on eighteen species 
belonging to eleven genera; Puccinia graminis secalis, according to 
Eriksson (41) on eleven species belonging to five genera and according 
to Stakman and Piemeisel (149) on twenty-three species belonging to 
nine genera; Puccinia glumarum secalis on Secale cereale and Triticum 
vulgare; Erysiphe graminis secalis on two species of Secale; and Puc- 
cima dispersa secalis on Secale cereale. 
Many of the specialized races, while in the main restricted to certain 
hosts, yet are able to infect to a greater of less extent a number of 
other plants. Generally these races are distinguished by their ability 
to fully infect certain hosts while their development on others is 
weak and limited. Very good illustrations of such races are found 
among several of the rusts. The various races of Coleosporium 
Campanulae are not sharply limited to definite hosts, but the hosts of 
one race may also be attacked by other races. The same is true of 
the races of Puccinia graminis, P. coronata, P. Ribesti-Caricis, Melamp- 
sora Larici-epitea and Uromyces Poae. 
