6 BOTANICAL GAZETTE [yULY 
diameter of 1.5™™. Some of these colonies transferred to tubes con- 
tinued to enlarge, became tubercular, and developed a yellow center 
3 or 4™™ in diameter. The whole colony often reached 1°™ in diam- 
eter. Sister colonies left in the plate (1 per square millimeter) failed 
so to develop, and it is evident that at even this density normal 
development is not attained. 
The colony is indeterminate in growth, and in plates its size is 
limited by the presence of adjacent colonies. 
SUMMARY REGARDING THE DENSITY FACTOR 
This factor produces different effects with the different species. 
It may inhibit pycnidial formation, resulting in naked spores; it may 
cause failure to develop color; it may limit the size of the colony; 
it may be without effect. 
There are many paired species of the imperfect fungi agreeing 
closely, except in the presence or absence of one character. These 
pairs often occur upon the same host, e. g., Seploria Lycopersici Speg. 
and a Cylindrosporium on the tomato; Cylindros poriumChrysanthemt 
E. & D. and Septoria Chrysanthemi Cav. on the cultivated chrysan- 
themum.3 Many other instances could be cited. The lack of fixity 3 
of such a structure as even the pycnidium throws doubt upon the © 
validity of such species as these and indicates the necessity of close 
comparative study. 
II. Density of mycelium: zone formation 
The formation of concentric zones is by many fungi one of the 
most conspicuous characters shown in culture. These zones may be 
3 VOGLINO, P., Diseases of cultivated chrysanthemums. Malpighia 15:329-341- 
1902. (Exp. Sta. Rec. 14:777. : 
HatsteD, B. D., Chrysanthemum leaf spot. Amer. Florist 10:263. 1894. (Exp. | 
Sta. Rec. 6:311.) 
Beaca, S. A., Leaf spot of chrysanthemum. Report of Horticulturist, N. Y- 
Exp. Sta. Rept. 1892:557-560. 
Hatstep, B. D., Report of fungus disease of plants. N. J. Exp. Sta. Report 
1891: 233-340. 
Saccarpo, Syll. Fung, 22542, m. 3497, 3498, 3757. 
TusBeur & Situ, Diseases of plants 478. 
Year Book U. S. Dept. Agr. 1906: 507. 
New York Agr. Expt. Sta. Rept. 14:529. 
New Jersey Agr. Expt. Sta. 1894: 36r. 
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