ILLUSTRATIONS 
PLATES 
Historical Relations or Sugar-Beet Seedlings and Phoma betas 
Page 
PLATE I. Fig. i.—Section of a sugar-beet seedling invaded by Phoma betae , 
showing distribution of the mycelium and the action of the fungus on the 
protoplasm and cell walls. Fig. 2.—Section of sugar-beet seedling show¬ 
ing characteristic action of Phoma betae on the cyptoplasm and nuclei and 
cell walls in cases of serious infection. Fig. 3.—Section of sugar-beet seed¬ 
ling, showing Phoma betae penetrating the cell walls and expanding in one of 
the cells. Fig. 4, 5, 6.—Abnormal nuclei from uninfected cells adjacent 
to invaded tissue of sugar-beet seedlings. 58 
Plate II. Fig. 1.—Section through a sugar-beet seedling which has recovered 
from an attack of Phoma betae , showing a young pycnidium of the fungus 
forming on the discarded, killed tissue. Fig. 2.—Longitudinal section 
through a sugar-beet seedling which had recovered from an attack of root 
sickness due to Poma betae , showing the presence of the fungus established 
in a condition of reduced virulence in the living cells. 58 
Perennial Mycelium in Species of Peronosporaceae Related to 
Phytophthora infestans 
Plate III. Fig. 1.— Cystopus candidus on Lepidium virginicum. Fig. 2.— A, 
The two leaves at the left show the amount of sporulation of Peronospora 
parasitica on leaves of Lepidium virginicum; B, the two leaves at the right 
show Cystopus candidus fruiting on leaves of Capsella bursa pastoris. Fig. 
3.— Peronospora viciae on Vicia sepium . 70 
Hibernation of Phytophthora infestans in the Irish Potato 
Plate IV. Phytophthora infestans: Infection of potato tubers. Fig. 1.— 
Cross section of a tuber which was infected with P. infestans and was 
planted in the greenhouse in rather dry soil. Fig. 2.—This tuber was inoc¬ 
ulated at the eye surrounded by the paraffin ring. Fig. 3.—Cross section of 
an infected tuber planted in sterilized soil in the greenhouse which devel¬ 
oped a shoot that became infected through the parent tuber. Fig. 4.—The 
small stunted shoot which grew from this infected tuber shows the pro¬ 
gressive discoloration caused by P. infestans growing up the stem. 102 
Plate V. Phytopththora infestans: Infection of a potato plant. 102 
Plate VI. Phytophthora infestans: Infection of potato shoots and plantlets. 
Fig. 1.—This shoot grew from a diseased tuber planted in the greenhouse 
under field conditions. Fig. 2.—This shoot, which had not reached the 
surface of the soil, grew from an infected tuber in the field. Fig. 3.—This 
plantlet was the progeny of a diseased tuber planted in the open. 102 
Plate VII. Phytophthora infestans: Infection of potato plants. Fig. 1.— A hill 
of potatoes having 13 shoots grown from a whole infected tuber in the field. 
Fig. 2.—In this hill with two shoots the fungus has reached the surface 
and killed its host. Fig. 3.—This shows the hill illustrated in figure 2, in 
its position in the row where it grew. 102 
Plate VIII. Phytophthora infestans: Infection of potato plots. Fig. 1.—A 
comer of the plots where infected seed potatoes were planted. Fig. 2.— 
The area within the white lines shows a spot where infection is much more 
prevalent than in the surrounding plants.. 102 
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