570 Journal of Agricultural Research voi.xv.no. w 



phloem alone. This condition might be explained by assuming that 

 the individual cells react differently toward the stimulus and that we 

 have a more or less complete antagonism in those groups of cells which 

 suffer only slightly or not at all. If, however, the toxin is localized or 

 the virus is produced in situ, differential necrosis of the phloem as well 

 as necrosis of certain cells of the cortex and pericycle becomes explainable. 



The accumulation of starch in the diseased leaves, together with the 

 reddish discoloration suggests, of course, inhibition in the process of 

 translocation. This nonremoval of synthesized food material may be 

 caused by lack of minerals or by the partial or complete stoppage of the 

 path of translocation for these substances. In many instances necrosis 

 of the phloem could in itself account for inhibition in translocation even 

 if the phloem of petiole and midrib is mostly normal. In such cases the 

 phloem of the stem, near the point of the insertion of the leaf, is usually 

 severely diseased, much more so than in any other region of the stem. 

 The nonremoval of starch from leaves where necrosis of the phloem is no 

 factor of importance has still to be explained. 



The rolling of the leaves and the characteristic xerophytic appearance 

 of the diseased plants is the resultant of many interrelated changes and 

 processes; such changes could not be produced by simple anatomical 

 disturbances; nor can the results be explained on merely a mechanical 



basis. 



LITERATURE CITED 



(i) AppeL, Otto, and Schlumberger, Otto. 



I9II. DIE BI,ATTROLLKRANKHEIT UND UNSERE KARTOFFEtERNTEN. Arb. Dcut. 



Landw. Gesell., Heft 190, 102 p., 13 fig., pi. (i fold.). Literaturu- 

 bersicht, p. 82-102. 



(2) Artschwager, Ernst F. 



1918. Anatomy of the potato plant, with special reference to the ontogeny 

 of the vascular system. In Jour. Agr. Research, v. 14, no, 6, p. 

 221-252, 4 fig., pi. 27-47. Literature cited, p. 251-252. 



(3) KtJsTER, Ernst. 



1916. PATHOLOGISCHE PFLANZENANATOMIE . . . Aufl. 2, 447 p., illuS. Jcna. 



(4) Orton, W. a. 



1914. POTAtO WILT, leap-roll, AND RELATED DISEASES. U. S. Dept. AgT. 



Bul. 64, 48 p., 16 pi. Bibliography, p. 44-48. 



(5) QuANjER, H. M. 



1913. DIE NEKROSE DES PHLOEmS DER KARTOFFELPFLANZE, DIE URSACHE DER 



BLATTROLLKRANKHEiT. In Mcded. Rijks Hoogere Land-, Tuin- 

 en Boschbouwschool [Wageningen], deal 6, afl. 2, p. 41-80, 9 pi. 



(6) 



I916. ON THE NATURE, MODE OF DISSEMINATION AND CONTROL OP PHLOEM- 

 NECROSIS (lEafroll) AND RELATED DISEASES. In Meded. Rijks 

 Hoogere Land-, Tuin- en Boschbouwschool [Wageningen], deel 10, 

 p. 91-138, 12 pi. 



(7) ScHANDER, R., and Tiesenhausen, M. v. 



1914. KANN man die PHLOEMNEKROSE ALS URSACHE ODER SYMPTOM DER 



BLATTROLLKRANKHEIT DER KARTOFFEL ANSEHEN? (ABSTRACT.) lit 



Ztschr. Pflanzenkrank., Bd. 25, Heft i, p. 16-18. 1915. Original 

 article in Mitt. Kaiser Wilhelms Inst. Landw. Bromberg, Bd. 6, 

 Heft 2, p. 115-124, 4 fig. 1914. 



