4 
WALTER SPURGEON BEACH 
forms with certain of their host-plants become compHcated by the existence 
of 'biologic forms' of the host-plants." Salmon found that in Bromus 
mollis there is a susceptible and an immune race with respect to four separate 
biologic forms of the mildew. 
G. M. Reed (24-29) has corroborated the results of Salmon and others, 
and has carried out extensive cross-inoculation experiments with Erysiphe 
graminis (27, 28, 2q) in which he has shown considerable variation in sus- 
ceptibility among the species and varieties of Triticum, Hordeum, Avena, 
and Secale, a few of which are immune. In Erysiphe cichoracearum upon 
Cucurbitaceae (25) he found but one biologic form, capable of growing 
upon various members of this host family. 
The more important instances of biologic specialization reported in 
other groups of fungi are as follows: by Stager in Claviceps (41), by Diedicke 
in Pleospora and its conidial stage Helminthosporium (5), by Gilbert in 
Plowrightia morhosa (ii), by Miiller in Rhytisma acerinum (20), and by 
Hesler in Sphaeropsis malorum (12). Shear and Wood (40) found that the 
races of Glomerella cingulata from different hosts vary somewhat in the 
vigor of their attack upon other hosts. Tests by Westerdijk (47) indicate 
the absence of biologic specialization among similar races of Sclerotinia 
lihertiana. Rands (23) has proved by cross-inoculation that the Alternaria 
of Datura and that of potato are not identical as some have supposed. 
With species of Septoria only a few investigators have worked. Levin 
(15) inoculated several plants akin to the tomato with Septoria ly coper sici. 
Definite small black spots without pycnidia appeared on potato, but no 
effect was seen on other plants. Norton (22) performed similar experiments 
in humid inclosures, and obtained infection upon several species of Solanum. 
A further discussion of this author's results will be given in a subsequent 
section. Stone (45) proved by infection that Septoria rihes and likewise its 
perfect stage Mycosphaerella grossulariae taken from Rihes nigrum will 
infect R. grossularia, R. rubrum, and R. oxyacanthoides. 
Montemartini (18) has concluded that parasitic fungi are extremely 
sensitive to the chemical composition of the nutritive medium on which 
they live, and that under its influence they acquire characters of adaptation, 
which attain to a certain fixity. In consequence fungi may become unable 
to flourish on species different from those to which they have accustomed 
themselves, or even on other portions of the same plant which they inhabit, 
or in different developmental stages of such plant or organ. This problem 
is further complicated by atmospheric conditions, and the influence thereof 
upon sensitivity to attack as well as upon the virulence of the infecting 
bodies. 
The review here given serves to illustrate the intricate nature of biologic 
specialization, and to remind one of the various factors to be considered 
in the interpretation of the results of inoculation experiments. 
