308 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Appearance of the Disease. 



A badly infected plant at first sight presents no uncommon feature 

 unless it be that the plant looks stronger than its fellows. On moving 

 aside the shoots, however, a corrugated or spongy mass of yellowish- 

 green tissue (the colour varying with the amount of chlorophyll 

 developed) may be found arising from the stems near or under the sur- 

 face of the ground. Inspection of many specimens reveals the fact that 

 the mass is a modified leaf, and all stages of it may be found, from 

 the mere wart to the unaltered leaf, or a warty mass with leaf-like 

 outline. The author once found part of the inflorescence infected. 

 In such cases infection has taken place when the shoot has pushed 

 its way through the infected soil, or the leaf has lain on it, and there 

 is no evidence that the fungus can make its way through the stem. 

 These surface masses are easily seen in late July and August, but 

 after that time they frequently rot, releasing the sporangia and leaving 

 only a dark shell, which is not very obvious. On lifting the plant some 

 or all of the tubers are seen to have similar outgrowths, but the colour 

 is that of the skin of the potato, although it varies with the distance 

 from the light, while tubers growing near the surface may push the 

 warts outside, which thereupon develop chlorophyll and become green. 

 A series of specimens will show that the warts arise in the bud or eye 

 of the tuber and they often become leaf-like. The intensity of the 

 infection depends to some extent on the amount of water in the soil, 

 and in a dry season tubers may be found with few or no warts, and 

 the haulm ma} 7 be unaffected, although it may be known that the soil 

 is thoroughly infected. The disease is not confined to any par- 

 ticular soil — sandy and clayey soils or medium loams all give rise to 

 diseased plants if infection has been introduced. 



Cause of the Disease. 



An examination with a pocket lens of the cut surface of a wart 

 shows reddish -brown lines just under the skin, and these are seen to 

 consist of numerous reddish-brown bodies. Under the microscope 

 these bodies, which the researches of Johnson (33) and Percival 

 (56, 57) have shown to be sporangia, vary from 30-70 /t in diameter, 

 and have thick dark brown walls, which are ridged and in certain 

 views look angular. These are the so-called " resting spores," and 

 are released into the soil when the warty masses rot. As already 

 mentioned, the organism was first recognized by Schilberszky (72) 

 in specimens from Upper Hungary, and he named it Chrysophlyctis 

 endobiotica. In England it first came under scientific notice when 

 M. C. Cooke (15, 16), Carruthers (3), Massee (48), Potter (58), 

 received specimens, and a controversy arose as to its identity with 

 Schilberszky's organism. The details are given in full in Horne's 

 paper (31), but the name stood until Percival (56) came to the con- 

 clusion that the organism belonged to genus Synchytrium and the 



