Mar. i, 1924 
Morphological Characters of Alternaria mali 
707 
The following measurements of 50 conidia from a 16-day-old culture 
of race B on corn-meal agar are of interest because of the long coni- 
diophores (isthmi): 
Average. 
2- septate (2 per cent), 21x8. 21x8 
3- septate (10 per cent), 22 to 39 x 7 to 9. ... 30x9 
4- septate (18 per cent), 32 to 42 x 8 to 9. 37 x 8 
5- septate (30 per cent), 32 to 52 x 8 to n. 40 x 9 
6- septate (22 per cent), 44 to 52 x 8 to 10. 48 x 9 
7- septate (14 per cent), 48 to 59 x 8 to 12. 54 x 9 
9-septate (4 per cent), 52 to 63 x 8. 58 x 8 
With longitudinal septation (16 per cent), width 9 to 12. . 10 
Without longitudinal septation (84 per cent), width 7 to 9. 8 
Conidiophores (isthmi) 6 to 59 x 3 to 5. 18x4 
Conidiophores having a length of more than 20 were 1 to 4 septate. 
Number of septa of all the conidia. 5. 22 
Dimensions of all the conidia. 43 x 8 
The larger conidia and conidiophores of race B were possibly due to 
the nutritional advantages incident upon their location in or at the sur¬ 
face of the culture medium. It should be noted that the measurements 
of race A and the parent are not greatly different. The differences 
between A and B were not due to differences of environment, since they 
were grown side by side in the same plate, but it is possible that the con¬ 
ditions attending growth on culture media may have acted as a stimulus 
to the disclosure of certain differences not apparent in nature. 
Mutations were also observed in other single conidium cultures of 
Alternaria mali from apple leaves and single conidium cultures of the 
Alternaria isolated from lilac leaves. On the other hand, species from 
cranberry and blueberry supplied by Dr. Neil E. Stevens and subse¬ 
quently grown by the writer from single conidia showed no tendency 
toward mutation. An Alternaria from blackberry supplied by Dr. B. O. 
Dodge showed two distinct forms from the first culture. Single conidium 
cultures were not used here, however, and it is possible that two distinct 
species were present. A culture of Alternaria tenuis supplied by Dr. 
Johanna Westerdyk showed no tendency toward variation, though grown 
in plate cultures with frequent transfers. 
SUMMARY 
Alternaria mali often enters apple leaves through injured or dead spots 
and forms about them characteristically crescent-shaped or circular 
enlargements. A brief discussion of some of the morphological characters 
of the genus Alternaria based on observation of species from apple, lilac, 
cranberry, blueberry, blackberry, and forsythia is given. A. mali is 
described more fully than formerly and more detailed measurements 
of conidiophores and variously septate conidia are given. Variants, 
considered as due to mutation, were found in “single spore” cultures of 
A. mali . 
literature cited 
(1) Bary, A. de. 
1887. COMPARATIVE MORPHOLOGY AND BIOLOGY OF THE FUNGI, MYCETOZOA AND 
bacteria. Trans, by H. E. F. Garnsey . . . Rev. by I. B. Balfour. 
525 p., illus. Oxford. Bibliographical footnotes. 
(2) Bonar, Lee. 
1922. AN ALBINO MUTATION OF THE DEMATIACEOUS FUNGUS BRACHYSPORIUM 
TRiFoui. In Science, v. 56, p. 226-227. 
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