386 • -lOURNAL OF THE ROYAL HORTIClTL'ru HAL SOOIMTY. 



3. Spofigospom may be present in the soil of 'd particular field or 

 farm, but the disease may not manifest itself to any extent. 



4. The addition of lime to the soil at Cleadon brought about an 

 increase in the amount of disease. 



DESCRIPTION OF FIGURES. 

 Figure 96. — Portion of plant affected with potato canker in its early stages. 

 Figure 97. — Plant affected with potato tumour due to Cliryso'plilyctis. 

 Figure 98.— Plant badly affected with potato tumour. 



Figure 99. — a. Potato showing nmnerous small warts — the warty stage of 

 potato canker. 



B. Potato attacked with CJirysojihlyctis, showing outgrowths at the "eye." 

 When the Sfongosfora warts seen at a are crowded together at the 

 " eye," an appearance resembling b, a, may be sometimes observed. 



c. Potato affected with S'pongos'pora solani. Particular attention should" 

 be given to the " eye " marked 6. 



D. Potato affected with Chrysophlyctis. The excrescences at c and d should 



be compared with that marked 6 in c. ■ 



e. Potato affected with Spongosjjora photographed somo hours after removal 

 from the soil. The difference in colour of the diseased spots in 

 A and e records an actual difference in colour when photographed. 



F. Potato affected with Chrysophlyctis. 



Figure 100. — a-d. Potato canker— various scabby appearances. 



e. Potato affected with brown scab — not caused by Spongospora. 



Figure 101. — a. Potato affected with Spongospora — powdery-scab stage. 



B. Potato showing curious button-like scars, sometimes left by Spongospora. 

 c, D. Potatos showing a broad, somewhat wrinkled band (&) affected with 

 Spongospora. ' ■ 



E. Potato affected with Chrysophlyctis for comparison with c. 



F. Potato showing hollow space (c) left after the spore-balls of Spongospora 



have fallen away. Compare with a, a. 



Figure 102. — a-d. Misshapen potatos affected with Spongosp)ora. 



E. Tuberous outgrowth [a) from the surface of a potato affected with 



Spongospora. 



F. An outgrowth similar to that shown in e, cut open; h, limit of brown^ 



zone containing the mature spore-balls of the organism; r, limit of 

 the milky-white zone containing the myxamoebte and " plasmodia " ; 

 d, boundary of the cut area. 



Figure 103. — a. Potato affected with Phytophthora — Cleadon, 1909. 



B. Potato affected with Phyto2iht]iora, showing small scabby spots — Cleadon, 

 1909. 



c. Potato affected with Spongospora, showing cracks characteristic of the 

 epidemic of Phytophthora in the previous year — Cleadon, 1910. 



D, Potato affected with Phytophthora, showing cracks — Cleadon, 1909. 



e. Potato affected with Phytop>hthora, showing scabby spots suggestive of 

 Sj)ongospora — Cleadon , 1909. 



F. Potato affected with Sj>(>)iij(>.<i)(>r(t- {'V\\i.]m\, 1910. 



