Apr. >z, 1923 
Occurrence and Significance of Phloem Necrosis 
245 
thus formed becomes filled with a brown deposit, which at a certain 
stage takes the lignin stain. Following the swelling of the wall there 
is often a disintegration of the wall substance. The swollen wall 
appears lamellate (PI. 4, A) and between the lamellae spaces are formed 
which are filled with a gummy substance. The cell content also 
degenerates and disappears in part or becomes transformed into a 
substance giving reactions similar to the interstitial substance described 
above. Following the death of the cell and the subsequent loss of turgor, 
the phloem elements collapse, unless rapid lignification lends suflftcient 
rigidity to the walls and prevents their being crushed by the surrounding 
tissues. 
CONCLUSIONS 
The phloem of the potato, like that of the majority of herbaceous 
plants, remains normal throughout the vegetative period and up to late 
maturity of the plant. Although it is not affected by extremes in envi¬ 
ronmental conditions, it nevertheless undergoes pathological changes 
under the effect of certain metabolic disturbances such as probably 
exist in the leafroll disease. These changes consist in lignification or 
obliteration of cell wall and content. However, while obliteration of the 
phloem is always observed in connection with leafroll, it is also an accom¬ 
panying phenomenon in other diseases. It is not so much its mere 
presence as its universality in distribution, coupled with the absence of 
necrosis in other tissues, which gives it a real diagnostic value. 
LITERATURE CITED 
(1) Artschwager, Ernst F. 
1918. Anatomy of the potato plant, with special reference to the on¬ 
togeny OF the vascular system. In Jour. Agr. Research, v. 14, p. 
221-252, 4 fig., pi. 27-47. Literature cited, p. 251-252. 
(2) - 
1918. Histological studies on potato leafroll. In Jour. Agr. Research, 
V. i 5 » P- S 59 - 57 o» pl- 35-45, pk C (col.). Literature cited, p. 570. 
(3) Bliesenick, Hermann. 
1891. USER DIE OBLITERATION DER siEbrOhren. 63 p., I pi. Inaug.-Diss. 
Berlin. 
(4) Boodle, L. A. 
1902. ON lignification in the phloem of helianthus annuus. In Ann. 
Bot., V. 16, p. 180-183. Bibliographical footnotes. 
(5) Esmarch, F. 
1920. DIE phloEmnekrose DER KARTOFFEL. In Ber. Deut. Bot. Gesell., Bd. 
37, p. 463-470. Bibliographical footnotes. 
(6) Quanjer, H. M. 
1913. DIE NEKROSE DES PHLOEMS DER KARTOFFELPFLANZE, DIE URSACHE DER 
blattrollkrankheit. In Meded. R. Hoog. Land-.Tuin-en Boi^h- 
bouwsc. Wageningen, Deel 6, p. 41-80, pi. 2-9. Bibliographical 
footnotes. 
(7) ScHANDER, Richard, and Tiesenhausen, M. v. 
1914. KANN man die PHLOEMNEKROSE ALS URSACHE ODER SYMPTOM DER 
blattrollkrankheit DER KARTOFFEL ansehen? In Mitt. Kaiser 
Wilhelms Inst. Landw. Bromberg, Bd. 6, p. 115-124, 4 fig. 
(8) Schumann. 
1890. BEITRAG ZUR ANATOMIE DES COMPOSITENSTENGELS. In Bot. Centbl., 
Bd. 41, p. 193-196. 
