32 
WALTER SPURGEON BEACH 
37. . On specialization of parasitism in the Erysiphaceae. III. Ann. Mycol. 3: 
172-184. 1905. 
38. . On the stages of development reached by certain biologic forms of Erysiphe 
in cases of non-infection. New Phytol. 4: 217-222. 1905. 
39. . Further cultural experiments with 'biologic forms' of Erysiphaceae. Annals 
of Botany 19: 125-148. 1905. 
40. Shear, C. L., and Wood, Anna K. Studies of fungous parasites belonging to the genus 
Glomerella. U. S. Dept. Agr. Bur. PI. Ind. Bull. 252. 19 13. 
41. Stager, R. Infectionsversuche mit Gramineen-bewohnenden Claviceps-Arten. Bot. 
Zeit. 61: 111-158. • 1903. 
42. Stakman, E. C. A study in cereal rusts. Minn. Agr. Exp. Sta. Bull. 138. 1914. 
43. Stakman, E. C, and Piemeisel, F. J. Biologic forms of Puccinia graminis on cereals 
and grasses. Journ. Agr. Res. 10: 429-495. 1917. 
44. Steiner, J. A. Die Specialization der Alchemillen-bewohnenden Sphaerotheca humuli 
(DC.) Burr. Centralbl. Bakt. 21: 677-736. 1908. 
45. Stone, R. E. Studies in the life histories of some species of Septoria occurring on Ribes. 
Phytopathology 6: 419-427. 19 16. 
46. Ward, H. M. Further observations on the brown rust of the bromes, Puccinia dispersa 
(Erikss.), and its adaptive parasitism. Ann. Mycol. i: 132-151. 1903. 
47. Westerdijk, J. Untersuchungen iiber Sclerotinia lihertiana als Pflanzenp^rasit. 
Meded. Phytopathologisch Lab. Willie Commelin Scholten 2: 1-26. 191 1. Am- 
sterdam. 
EXPLANATION OF GRAPH i 
This graph represents variations in spore length in Septoria verbascicola B. & C. and 
S. tritici Desm. under a number of different conditions. The measurements of spores are 
indicated in microns by the base line, each space representing one micron. The frequency 
is indicated on the perpendicular lines, each space representing one spore. The measure- 
ments are at intervals of 2.4 microns, and for each curve 200 spores were measured. 
A and B represent ranges in length of spores from a single culture of S. verbascicola 
upon onion agar; in A the spores were from the lower portion of the colony which was 
moistened by the small amount of water on the agar, while in B the spores were from the 
upper edge of the colony where the agar was drying. C represents spores from spots of 
leaves of Verbascum blattaria in the field where the light exposure was intense; Z), spores 
from shaded rosette leaves of the same host in the field; E, spores from the same host kept 
under very humid conditions in the greenhouse; F, spores of the same fungus growing upon 
Scrophularia marilandica, conditions as in E. 
G represents the range of spore length of S. tritici upon the upper stem leaves of natu- 
rally infected wheat plants in the field in July; H, spores of the fungus from the same field 
taken from the basal leaves of volunteer wheat in January. The plants of wheat were dug 
up and kept for a few days in a closed collecting can in the greenhouse. 
* EXPLANATION OF PLATE I 
Preparatory to photographing, the leaves were treated with hot alcohol to remove the 
chlorophyll, but this process produced no apparent change in the character of the disease 
spots. The leaves were then softened in 50 percent glycerine and pressed. 
Fig. I. Disease spots of Septoria polygonorum Desm. upon Polygonum pennsylvanicum. 
Natural infection. 
Fig. 2. Disease spots of the same fungus upon P. persicaria. Natural infection. 
Fig. 3. Disease spots of the same fungus upon P. lapathifoliun?: Natural infection. 
Fig. 4. Disease spots of the same fungus upon P. orientale. Artificial inoculation. 
Fig. 5. Disease spots of Septoria malvicola E. & M. upon Malva rotundifolia. Arti- 
ficial inoculation. 
