ELISHA MITCHELL SCIENTIFIC SOCIETY. Ill 



(see Fig. 38, Plate VI) When tlie potatoes reniain in tlie ground 

 for some time, or have been infested for some time dnrinor their 

 growing condition, large warty growths are sometimes formed, 

 as represented in the upper right-hand figure in Plate I. Again 

 the tubers which have lain in the ground after maturity and 

 sprouted ("volunteers") being badly infested, the young sprouts 

 are attacked and large galls produced on them close to the sur- 

 face of the tuber. In tijese cases [)itted ducts are developed to 

 a very great extent and a large majority of the mature female 

 cysts are surrounded by an intricate net-work of these ducts. Id 

 making sections of such galls many of these cysts are cut through, 

 and by removing the remains of the cyst there is the appearance 

 of a beautiful microscopic basket woven from the ducts and 

 imbedded in the looser parenchymatous tissue near by. In the 

 galls of the peach root, beside the special structural derangements 

 which could be classed under the head of the foregoing charac- 

 ters, there appears in many of the nearly mature or old female 

 cysts a secondary growth of pseudoparenchymatous tissue fi'om 

 the inner periphery of the cavity, which in some cases nearly 

 fills the cavity with tender, loosely compacted cells, so that the 

 cyst is often deformed by the pressure of these ingrowing cells, 

 and in very old ones the larvne lie in different places in the tissue. 

 It requires in some cases very careful seirch to find a female cyst 

 which can be removed and recognized as the female of Heterodera. 

 Comparison of the External Appearance of the 

 Root-gall Disease of the Potato with " Potato Scab.'' — 

 In some of the peculiarities of the disease in the potato tubers 

 caused by Heterodera radiGWola there is a striking resemblance, 

 especially in the earlier stages, to the effects of the disease called 

 ''potato scab" and attributed by Brunchorst* to the action of a 

 parasitic organism of very simple structure which he calls Spon- 

 gospora Solani, and considers to be closely allied to the organism 

 called by Woroninf Plasmodiophora Brassicce, which causes the 



*Ueber eine sehr verbreitete Krankheit der Kartoffelknollen. In Bergens Museums 

 Aarsberetning for 188G, p. 219. 

 See also "Potato scab," J. E. Humphrey, Mass. State Exp. Station, Gth Annual Report, 



1888. 



fPringsheim's Jahrbucher fur wisseuchaftliche Botanik, Vol. XI, p. 548. 



