268 
Journal of Agricultural Research 
Vol. VIII, No. 7 
Table V. —Constants for chlamydospores and oospores of species of Phytophthora 
CHEAMYDOSPORES 
Species. 
Mean. 
Median. 
Mode. 
Standard 
deviation. 
Skewness. 
P.faberi . 
a 
A* 
A* 
A* 
A* 
38. 98±o. 167 
38. 62±0. 2X1 
37- 90 
4- 97±o. 118 
0. 2173 ±0.0386 
P.jatrophae . 
32. 89± . 180 
32- I3± • 228 
30. 61 
5-36± .128 
• 42S7± *0332 
P. nicotianae . 
28. 83 ± .203 
27-35± -256 
24- 39 
6.03± . 144 
•7383 ± -0254 
P. parasitica . 
31.15 ± . 133 
30. 72± . 167 
29. 86 
3-92± .093 
•3293± • °359 
OOSPORES 
P. caciorum (Phyllocactus sp.) 
P, caciorum (Panax sp.). 
PJagi .. 
P. syringae . 
P. phaseoli . 
P. arecae . 
P. erythroseptica . 
26. 78 ±0.08 r 
26. 67±0.104 
26. 45 
2 - 40 ± 0 . 057 
o'. i374±o. 0401 
27. 36± .084 
27- r5± 
. 108 
26. 73 
2. 5o± . 060 
. 2576± . 0377 
30. 22i . 125 
30. IO± 
• 159 
29. 86 
3-71± . 088 
. 0970± . 0407 
29.50± . 108 
29 - 54 ± 
■137 
29. 62 
3.19± . 076 
— .0376± .0412 
25- 55 ± -088 
25- 74 ± 
*113 
26.12 
2. 60± . 062 
.2i9i± .0386 
32. 42± . 152 
32. OI± 
• 193 
3 1 -19 
4. 53 ± . 108 
• 375 i± ■ °374 
35. 78± . 127 
35 * 7 °± 
. 161 
35 - 54 
3. 77 ± -090 
. 0636± . 0410 
The ratios of the length to the width of the 400 conidia measured are 
arranged into classes in figure 8. By the use of these data, representing 
400 ratios of length to width of conidia, the means and the standard 
deviation of the ratios for each species were determined. The results 
are shown in Table VI. From this it will be clearly seen that the ratio 
of the length to the width of the conidia can be made use of in the separa¬ 
tion of the species; and, in fact., it is suggested that a similar system of 
measurements in other fungi may perhaps be made use of in delineating 
species. 
Table VI. —Constants as calculated from class ratios of length to width of 400 conidia of 
species of Phytophthora as shown in figure Q 
Species. 
Means. 
Standard 
deviation. 
Species. 
Means. 
Standard 
deviation. 
PJagi . 
P. phaseoli ... 
P.jatrophae . 
P. caciorum (Panax sp.) 
P. erythroseptica . 
P, arecae . 
P. syringae . 
A* 
1.25 ±0.004 
1.40± . 006 
I. 28± . 006 
1. 34± .006 
1. 57± . 008 
1. 59± . 009 
I. 49± -on 
a 
0. no±o. 003 
. i7o± . 004 
. i68± . 004 
. 165± . 004 
. 229± . oos 
. 278± . 007 
■ 3i4± *007 
P. infestans . 
P. parasitica . 
P. caciorum (Phyllocac¬ 
tus sp.) . ! 
P. faberi . 
P. nicotianae . 
A* 
i-45±o. 006 
I. 82 i .009 
1. 39± • 005 
1. 47± .007 
1. 25± .006 
t* 
0. l89±o. 005 
. 259± . 006 
. 149± . 004 
. 197 ± - 005 
. I7l± . 004 
Reitz and Smith (26) make the following statement regarding the 
significance of probable errors: 
In the comparison of two statistical results, the difference between the two results 
compared to its probable error is of great value. In general, we may take the probable 
error in a difference to be the square root of the sum of the squares of the probable 
errors of the two results. 
If the difference does not exceed two or three times the probable error thus obtained, 
the difference may reasonably be attributed to random sampling. If the difference 
between the two results is as much as five to ten times the probable error, the prob-' 
ability of such differences in random sampling is so small that we are justified in say¬ 
ing that the difference is significant. In fact, a difference of ten times its probable 
error is certainly significant in so far as there is certainty in human affairs. 
