108 JOURNAL OF THE 



has been said to show that great variation prevails and to give 

 the typical forms about which all may be easily grouped. A 

 list of the diseased plants whicli have thus far been found in 

 this section will be given in Section VIII, while a comparison 

 of the disease with some other characters and diseases of plants, 

 wnth which it might be confounded upon external examination, 

 will be made after the discussion of the microscopic details of 

 the diseased tissues. 



Histological Characters {See also references heloxo^). — 

 The w^orms locate preparatory to passing into the cystic state at 

 various depths in the tissues of the root. They are not confined 

 to any particular tissue element or system, but locate in the vas- 

 cular tissue of tlie central cylinder, the cambium, parenchyma, 

 or even in the bark, so that the body of the mature female cyst 

 is frequently only protected by a thin layer of the dead peripheral 

 tissue or sometimes is even exposed. They seem to flourish bet- 

 ter, however, in or near the softer tissues of the root. It is a 

 very common thing to find dead undeveloped female cysts, the 

 majority of which I have always found in the woody tissue of 

 the central cylinder. Possibly surrounded as they are by the 

 harder, more compact tissue there is less certainty of the male 

 reaching them for fertilization. This, however, is only a sug- 

 gestion. I have not demonstrated it. All of the tissue elements 

 in the diseased roots undergo hypertrophy, while some of them 

 are subject to special changes in form as well as direction of 

 growth. 



The parenchyma cells which normally have their tangential 

 diameter greater than the radial are so changed that the radial 

 diameter is the greater. This change in form of the parenchyma 

 cells seems to obtain in nearly all of the paienchyma in the gall 



*G()0<lixIe, r^hysiologifal Botany, Vol. 11, Gray's Hotanioal Text-books. 



Van Ticgliem, Traite de Hotaniiiue, Deiixienr)e Ivlition, Fascicule 5. 



Muller, Mittlieilungen iiber die unseren Kulturptlanzen scliadlieiie, das Gesehlecht 

 Heterodera bii<lenden VViumer, Landwirthscliattliehe Jahrbuclier, Bd XIII, Heft, I, 

 1884. 



.lahresbeiicht fur Wiss. Bot. (Just), 1876, p. 1'235. 



Idem, 1877, pp. .')l()-.517. 



Idem, 1878, p. 174. 



Idem, 1878, p. 109. 



%Soianer, Pt1an/,enl<rankhoiten, Zweite .\nt1age, Vol. I. 



Frank, Kianklieiten der Ptianzen, and others. 



