May 19,1923 
Statistical Study of Biologic Forms 
541 
used throughout the entire period of the work. The illumination for the 
microscope was derived from artificial light of uniform intensity. The 
effect of refraction was eliminated as far as possible by mounting the 
material in drops of water of approximately equal size. It also was 
attempted to maintain the quantity of water on the slide nearly constant 
while the measuring of a given population of spores was in progress. 
In order to make the measurements of a given group of spores represen¬ 
tative and significant, a sufficient number of measurements must neces¬ 
sarily be made. It was found that in the case of aeciospores a minimum 
of 50 measurements was required. In the case of urediniospores and 
teliospores at least 100 measurements were necessary. Greater numbers 
than these did not seem to add materially to the value of the results ob¬ 
tained in the present investigation, although perhaps they might have 
been useful in some cases. The longitudinal measurements of teliospores 
were made from the exterior of the apex to the point of attachment of 
’ the pedicel, whereas the transverse measurements were made across the 
septum separating the two cells. 
COMPARATIVE MORPHOLOGY OF BIOLOGIC FORMS OF PUCCINIA 
GRAMINIS 
The following figures show the dimensions of spores of Puccinia 
graminis and P. phleipratensis ^ as given by several different workers, 
who made their studies at different times. 
TablK I.— Spore dimensions of P. graminis and P. phleipratensis as given by various 
authors 
Range of variation for length and width (in microns). 
Authority. 
P. graminis. 
P. phleipratensis. 
Aedo- 
spores. 
Urediniospores. 
Teliospores. 
Urediniospores. 
Teliospores. 
Eriksson and 
Henning (j, 
p. 25afdi^). 
McAlpine (5, px 
tp.t\ 
014--26 
&I 7 - 4 oXi 4~22 
20-36 Xi4“i8 
^ 35 -< 5 oX 11-22 
35-63X14-25 
35-65X15-20 
34- 60X12-22 
35- 60X12-22 
18-27X15-19 
38-52X14-16 
Plowright (<?, p. 
15-25 
14-26 
14-26 
Saccardo (u, v. 
7, p. 622, and 
V. II, p. 204), 
Sydow (15, p. 
6g$ and ^8j). 
24-45X14-21 
22-42X16-22 
18-27X15-19 
18-30X15-20 
35-52x14-16 
38-52x14-16 
a The aedospore measurements are for range of variation in the diameter of these spores. 
& These dimensions represent the extremes in range of size of two sets of measurements made by the 
authors. 
< P. graminis phleipratensis (E. & H.) Stak. and Piem. is dted in this instance as P. phleipratensis Erikss. 
and Henn. because the measurements quoted were obtained from sources in which this biologic form of 
stem rust was treated as a separate spedes. 
