442 
JOHN A. ELLIOTT 
actively engaged in descriptive mycological work. On one slide of 
Pleurosigma angulatum Sm., a single frustule was enclosed in a circle 
and indicated; on a second slide two spores of Alter naria fas ciculata 
were similarly indicated. A third slide of A. fasciculata contained 
several hundred spores. Identical typewritten directions were sent 
to each one who made the measurements, asking that no more care 
be used than- would ordinarily be taken in measuring for the purpose 
of describing a new species. A tabulation of results follows: 
Table A. 
Ob- 
server 
Eye- 
piece 
Single Frustule 
of 
One Spore of 
One Spore of 
Many Spores of 
Many Spores o£ 
No. 
Value 
P. ajigitlaiit7ii 
Alternaria 
Alternaria 
Alternaria 
Phoma 
I . . . . 
2.4 
285.6X45-6 
48 X7-2 
19.2 X9.6 
12-36 X 6-1 2 
2-5 X 1-2 
2 . . . . 
2.4 
284.4X46.8 
49.2 X6 
19.2 X9.6 
14-36 X 9-1 2 
3-4X2-3 
3 • • • • 
1.8 
284.4X45-9 
50.6X7.2 
19.8X9-9 
II-4I X6-I3 
4 . . . . 
3.16 
282 X46.5 
48 X7.5 
1.9-5X9.5 
10.5-24x7. 5-13 
5-6X1.5-2 
5 • • • • 
34 
282 X46 
48 X7 
20 X 10 
17-34x7-10 
6 .... 
3-2 
280 X45 
48 X7 
20 X7 
13-29 X 9-1 1 
4-8X2-3.5 
7 .... 
4- 
280 X44 
48 X7 
20 X9 
20X9 
5-6X2-2.5 
8 .... 
3-2 
276 X45 
48 X8 
21 X7 
12-35x9-12 
5-9X2-3 
9 .... 
10. 
275 X50 
13-35x7-11 
10 . . . 
3-2 
275 X45 
47 X7 
20 Xio 
12-33 X 6-1 2 
3-8X2-3 
II . . . 
3- 
270 X48 
50 X7-5 
21 X9-5 
1 5-40X8-1 2 
5-8X3-5 
Variation . . . 
15-6X6 
3.6X2 
1.8X3 
6.5-17X3-3 
3-4X2-3 
Variation %. 
5 X12 
7 X25 
8.5X30 
43-41 X 33-23 
60-44 X 66-60 
The second column gives the value of the smallest division of each 
eyepiece micrometer in micromillimeters. All the measurements 
given in the table are in microns. The arrangement is according to 
the maximum measurement given for Pleurosigma angulatum. 
The third, fourth and fifth columns show the variations in measure- 
ments when all, without any doubt, were measuring the same things. 
The variation is least in the longest measurements, being a little over 
5 percent in the greatest length given, and greatest in one of the two 
shortest measurements, amounting to 30 percent in the width of the 
spore indicated in the fifth column. That this variation is not due 
to the eyepiece used is shown by the fact that observer No. 10 who 
returned the lowest measurement for the long spore, column 4, also 
returned the highest measurement for the width of the spore given in 
column 5. The variations given for the Phoma spores are the greatest, 
being 66 percent for the shortest measurement and 44 percent for the 
longest measurement. In this case each mycologist made his own 
microscopic preparation. 
