706 
Journal of Agricultural Research voi. xxvii, No. <> 
B parts of the growth were usually much the larger. From the fifty- 
eighth to the sixty-ninth and last selection B remained constant. (PI. i, A, 
PI. 2, A, B.) 
We thus have two races arising from a single conidium, neither of which 
in culture is exactly like the parent. A lacks the aerial hyphae of the 
parent, while B fails to produce the thin carpetlike layer bearing charac¬ 
teristic conidia, producing, instead, the long slender spores at or beneath 
the surface of the culture medium. B grows more rapidly than A. 
There was no chance that A and B were from a mixed or contaminated 
culture, for they were not only the progeny of a single conidium, but of 
a succession of 15 singly selected conidia. 
Brierley (j) suggests that while variations in the “Fungi Imperfecti’* 
may be due to mutation, they may perhaps be more wisely interpreted 
in terms of the splitting of an originally impure genetic constitution or 
of gametic or somatic segregation from heterozygotes. In fungi not 
known to have a sexual stage, he suggests the possibility of genetic con¬ 
tamination by the fusion of hyphal cells. Until such contaminations 
can be shown to occur, it seems more logical to consider the aberrant 
strains as due to mutation while admitting the possibility of genetical 
contamination. The fact that neither of the two races of Altemaria 
was exactly like the parent lends some support to the genetical contami¬ 
nation theory. 
The following measurements were obtained from 50 conidia of each 
race taken at random from nine-day-old cultures growing side by side 
in a corn-meal agar plate. Conidial measurements are in microns and 
do not include conidiophores (isthmi). Unless otherwise specified the 
word “septate” means “transversely septate.” 
1- septate (4 per cent), 9 to 13 x 7 to 8. 11 x 8 
2- septate (26 per cent), i5to2ix7ton . 18 x 8 
3- septate (34 per cent), 21 to 28 x 7 to 11. 23 x 9 
4- septate (10 per cent), 27 to 36 x 8 to 12.32 x 10 
5- septate (18 per cent), 34 to 38 x 8 to 12.35 x 9 
6- septate (6 per cent), 38 to 42 x 9 to 12.39 x 10 
7- septate (2 per cent), 42 x 11..42 x n 
With longitudinal septation (36 per cent), width 8 to 12.. 10 
Without longitudinal septation (04 per cent), width 7 to 11. 8 
Conidiophores (isthmi) 4 to 6 x 3 to 6... 5 x 4 
Number of septa of all the conidia..... 3. 38 
Dimensions of all the conidia. 26 x 9 
RACE b 
Average. 
3- septate (12 per cent), 27 to 34 x 8 to 12.32 x 10 
4- septate (18 per cent), 34 to 42 x 8 to 9. 39 x 9 
5- septate (22 per cent), 38 to 57 x 7 to 9. 45 x 8 
6- septate (18 per cent), 40 to 55 x 8 to 12. 48 x 9 
7- septate (20 per cent), 57 to 67 x 7 to 13.60 x 10 
8- septate (4 per cent), 76 x 9 to 10.76 x 10 
9- septate (4 per cent), 63 to 80 x 11. 72 x n 
10- septate (2 per cent), 88 x 10..88 x 10 
With longitudinal septation (18 per cent), width 10 to 13. 12 
Without longitudinal septation (82 per cent), width 7 to 10. 9 
Conidiophores (isthmi) 5 to 14 x 4 to 6.. 8x5 
Number of septa for all the conidia. . ‘... 5. 54 
Dimensions of all the conidia..... 49 x 9 
