Mar. i, 1924 
Morphological Characters of Alternaria mail 
705 
From zonate spots on leaves of the common lilac growing near the 
apple trees at Arlington Experiment Farm, from which Alternaria 
mali was obtained, an Alternaria was isolated whose conidial meas¬ 
urements closely approximate those of Alternaria mali. In corn-meal 
agar cultures, however, it forms a thick olive green mat over the 
medium which is quite different from any observed growth of Alternaria 
mali. 
VARIATIONS IN ALTERNARIA MALI 
Variations, mutations, and races or strains among species of the 44 Fungi 
Imperfecti” have been noted by Bonar (2), Brierley (j), Burger (4), 
Crabill (£), La Rue ( 12 ), Shear and Wood (r£), Stevens (20), and 
others. The observation that many of the conidia of Alternaria mali 
have verrucose walls induced the writer to attempt to secure by selection 
a race having smooth conidia exclusively and another having verrucose 
conidia only. Starting with the progeny of a single conidium, selections 
of nonverrucose conidia were made through one series, while in another 
series attempts were made to select those having the highest degree of 
verrucosity. The method of isolating the selected spores has been 
described by the writer (17) in a previous publication. It was thought 
that continued selection might bring success, but after 22 generations, 
covering a period of two years, no difference in verrucosity could be 
noted between the conidia of the two series. The results of these selec¬ 
tions agree with those obtained by La Rue ( 12 ) in his selections for spore 
length and length of spore appendages in Pestalozzia guepini. It is 
possible that environment is the sole reason for the variation in verru¬ 
cosity, but the difficulties surrounding such attempts at selection are 
very great and no conclusion should be drawn. One can not be sure that 
out of all the conidia produced in the selected culture he is choosing 
those showing the greatest verrucosity. Neither can he be certain that 
the conidium which he considers as smooth might not become verrucose 
When older. Thus he may be simply selecting along an average. It 
must also be remembered that a single conidium of Alternaria is really 
not a single but a composite conidium usually consisting of many parts 
each capable of independent germination. The chance for variation 
in the progeny of a single conidium accordingly may be very great. 
While carrying on this work the writer observed a plate culture in 
which one section of the growth appeared quite different from the re¬ 
mainder. In this part, which will be designated as “A,” practically no 
aerial mycelium was produced, but there was a dark carpetlike mass 
over the surface of the medium, with olivaceous conidia produced in 
large numbers. The remainder of the growth, which will be designated 
as 44 B,” had abundant gray aerial mycelium with a scant production of 
long amber-colored conidia occurring in long chains running along the 
surface of the medium and parallel to it (fig. 1, E, F). Selections 
were made from each of these two forms for the purpose of attempting 
to establish 44 pure lines.” Transfers were made weekly from the growths 
of previous transfers showing the greatest growth of A and B, respectively. 
The selections were grown side by side, one of A and one of B on corn- 
meal agar in the same Petri dish. From the first, selection A showed but 
little tendency to break up into A and B. After the tenth selection it 
came true until the cultures were discarded. B broke up into A and B 
sections with great constancy during the first 57 selections, though the 
