244 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9 
Summary 
It has been commonly supposed that no crushing, or alterations in- 
volving a change in the chemical composition of the cell wall, occurs in the 
mature phloem of herbaceous angiosperms, although extensive alterations 
are known to take place in the mature woody stems of gymnosperms and 
angiosperms. It has been found, however, that within the series Tubuli- 
florae of the family Compositae, extensive lignification of the phloem 
parenchyma takes place in a number of species belonging to several dif- 
ferent genera. These elements appear to retain their functional activity. 
The structure of the sieve tubes and companion cells is not aflPected. 
The writer wishes to acknowledge the advice and assistance received 
during the course of the investigation from Dr. L. H. MacDaniels, of the 
Department of Pomology, New York State College of Agriculture, and 
from Dr. Ernst Artschwager, United States Bureau of Plant Industry, 
Washington, D. C. 
Department of Botany, 
New York State College of Agriculture, 
Cornell University 
BIBLIOGRAPHY 
de Bary, A. Comparative anatomy of the vegetative organs of the phanerogams and ferns 
English translation by Bower and Scott, p. 542. Oxford, 1884. 
Bliesnick, H. Uber die Obliteration der Siebrohren (Thesis). Berlin, 1891. 
Boodle, L. A. On lignification in the phloem of Helianthus annuus. Annals of Bot. 16: 
180-183. 1902. 
. Lignification of phloem in Helianthus. Annals of Bot. 20: 319-321. 1906. 
Moeller, J. Uber die Entstehung des Akacien-Gummi. Sitzungsber. K. Akad. Wiss. 
Wien Math.-Naturw. Kl. 72^: 219-230. 1875. 
Gudemans, C. A. J. A. Das Hornprosenchym Wigand's. Bot. Zeit. 20: 43-44. 1862. 
Rauwenhoff, N. W. P. Observations sur les caracteres et la formation du liege dans les 
Dicotyledones. Ann. Sci. Nat. Bot. V, 12: 347-364. 1869. 
Schumann. Beitrag zur Anatomic des Compositenstengels. Bot. Centralbl. 41 : 193-196. 
1890. 
Tschirch, A. Angewandte Pflanzenanatomie, pp. 342-352. Vienna and Leipsic, 1889. 
Wigand, A. Ueber die Deorganisation der Pfianzenzelle. Jahrb. Wiss. Bot. 3: 11 5-182. 
1863. 
EXPLANATION OF PLATE XIII 
Fig. I. Transverse section of phloem group from the stem of Gnaphalium poly- 
cephalum. Note contrast between lignified parenchyma and darkly stained, unlignified 
sieve tubes. 
Fig. 2. Transverse section, stem of Aster panicnlatiis , showing portions of the bundle 
cap, protophloem, and secondary phloem. 
Fig. 3. Enlarged view of a portion of the phloem group shown in figure 2. 
Fig. 4. Longitudinal section of the phloem of the stem of Aster ?iovae-angliae, show- 
ing unlignified sieve tubes {s) and lignified parenchyma (x). 
