Feb. 12,1917 
Studies of the Genus Phytophthora 
267 
Where the skewness is positive, the curve is more spreading on the side 
of large-sized individuals than in the opposite direction. In general 
this would point to the fact that the same conditions which favor the 
production of large individuals in the class as a whole is also more 
favorable to the production of exceptionally large individuals than 
exceptionally small ones. 
Table IV .—Constants for length and width of conidia of Phytophthora spp. 
LENGTH 
Species. 
Mean. 
Median. 
Mode. 
Standard de¬ 
viation. 
Skewness (ap¬ 
proximate). 
P.fagi . 
P. phaseoli . 
P, jatrophae . 
P. eactorum (Panax sp.) . 
P. eactorum (Phyllocactus sp.) . 
P. erythroseptica . 
P. arecae . 
P. syringae . 
P. infestans . 
P. parasitica . 
P. faberi . 
P. nicotianae . 
M 
33- 6s±o. 210 
27. 87± .195 
49- 65 ± .328 
36. 62± . 181 
37-69± .233 
44 * 85 i *303 
47 - 92 ± -327 
39-86± .374 
27- 08± • I 4 S 
43 - 64± .271 
48. 52 ± . 198 
37 * 58± -274 
A* 
33* *9±o. 264 
27.3i± .245 
49 * 79 i *413 
35- 46 ± • 228 
36- 03 ± .293 
45- 88± . 380 
46. 83± .411 
38. 5©± -470 
26. 78 ± . 183 
42. 88± .341 
48. 09± .250 
37. 62 ± .344 
U 
32- 28 
26.19 
50.08 
33 - 14 
32. 70 
47 - 93 
44-65 
35 * 79 
26.19 
41* 36 
47 - 23 
37 * 70 
6. 23 ±0.148 
5 - 77 ± -137 
9 - 73 ± *232 
5 - 37 ± • 128 
6. 91 ± . 164 
8. 98 ± . 214 
9. 70± . 231 
11. io± . 264 
4.3idt . 102 
8. o5± . 191 
5. 88± . 140 
8.12± . 193 
/* 
o.o2i9±o. 041 
. 2912 dh .036 
—. 0447 ± .041 
• 6478± .027 
. 7724± . 025 
— - 3432 ± .035 
• 3370 ± .035 
.3663 d: .035 
.2054± .039 
• 2833 ± .037 
. 2193 ± .038 
—. 0148 db .041 
WIDTH 
p. fagt . 
25.67 ±0.146 
25. 47±0* 185 
25.08 
4. 33 ±0.103 
0-1351 ±0. 040 
P. phaseoli . 
19.05± . 105 
18. 86± . 134 
18.48 
3. I2± .075 
. i826d: . 039 
P. jatrophae . 
37 * 55 ± -279 
36. 92 ± *350 
35 - 67 
8. 27± . 197 
.0227± .041 
P. eactorum (Panax sp.). 
26. o6± . 109 
26. 09± . 139 
26. 16 
3-24± .077 
—-0324± .041 
P. eactorum (Phyllocactus sp.). 
25. 72± . 120 
25 - 57 ± -153 
25.27 
3-57=b *085 
. I244± , 040 
P. erythroseptica . 
27. 65± .177 
27. i6± • 223 
26. 20 
5. 25± .125 
. 2750:$: . 037 
P. arecae.. . 
30. 05 ± . 186 
29. 8s± .234 
29 - 45 
5 - 5 o± .131 
. 1090± . 040 
P. syringae . 
25 - 33 ± -152 
25. 61 ± . 192 
26. 18 
4. 5®± • 107 
—. i900± . 039 
P. infestans ... 
18. 2?± . 102 
18. os± . 130 
17. 61 
3-03± .072 
. 2i8i± . 038 
P, parasitica . 
23 * 39 ± *147 
22. 74± . 186 
21.45 
4* 37± • 104 
<4428± .033 
P. faberi . 
32. 29 ± .159 
31. 40± • 201 
29. 63 
4 - 73 ± • 113 
. S 6 i 5 ± *029 
P. nicotianae . 
29. 95 ± • 230 
29. 84± . 289 
29. 63 
6-8i± .162 
• 0463± .041 
Means and standard deviation for the diameters of the chlamydo- 
spores and oospores are given in Table V. The smallest mean of the 
diameter of chlamydospores is that of P. nicotianae , with a standard 
deviation of 6.03 ±0.144 while P. faberi has the largest mean diameter, 
with a standard deviation of 4.97 ±0.118 fx. P. faberi can well be sepa¬ 
rated from the three other forms producing chlamydospores by its larger 
chlamydospores. The differences in size of the oospores are less strik¬ 
ing than those of the conidia, and the variations, as Seen from the stand¬ 
ard deviation, are likewise less. It has already been pointed out that 
P. phaseoli , P. arecae , and P. erythroseptica can be separated from the 
remaining forms in this table by morphological differences in the oospores, 
skewness being positive in all the forms with the exception of the oospores 
of P. syringae . 
