[Vor. 8 
6 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
by others as well as by the writers appears sufficient to justify 
the conclusion that many of the variations observed and reported 
here are not entirely due to any effect of simple environmental 
factors.” Further, they said: “The work of Jennings (711) 
with Paramecium and that of Barber (07), Will (90), Beijer- 
inck (97) and Hansen (’00) on yeasts, as well as that of other 
authors cited by Pringsheim ('10), demonstrate at least one 
thing, and that is the actual existence of rather distinct races or 
strains within species. These races possess more or less dis- 
tinetive and constant morphological or physiological character- 
istics which are generally inherited by their progeny and are 
apparently not primarily dependent upon environmental con- 
ditions.” Referring to the common rust of wheat, Stakman 
(14) says: “On the most resistant varieties, such as Khapli, 
the spores are often small in size and sometimes abortive.” 
From a study of biologie specialization in the genus Septoria 
Beach (19) observed that certain species are differentiated 
into biologie forms. According to him, disease characters as 
manifested by the host and some morphological characters of 
certain species of Septoria vary with the host and with environ- 
mental conditions and are therefore unreliable in taxonomy. 
Concerning the specialization of rusts, Klebahn (17) expressed 
an opinion, which unfortunately I have been unable to see in 
the original, but from the abstract by Matouschek (719) the 
following is suggestive of the position taken: “Die fluktuier- 
enden Variationen und die Mutationen sind ja Veränderungen, 
die, wenn auch vielleicht von der Aussenwelt beeinflusst, aus 
dem inneren Wesen des lebenden Protoplasmas hervorzugehen 
scheinen—und diese spielen bei Entstehung der Formenunter- 
schiede vielleicht eine gróssere Rolle als bei der Ausbildung der 
biologischen Verschiedenheiten. ” 
I should not neglect to mention also such studies as those of 
Stager on Claviceps, of Diedicke on Pleospora, of Gilbert on 
Plowrightia, of Müller on Rhytisma, and of Hesler on Sphae- 
ropsis malorum, etc. 
SOURCE OF MATERIALS 
All the strains obtained by me were first isolated by using 
potato agar, as this medium is very suitable for the mycelial 
