STUDIES ON THE PHLOEM OF THE DICOTYLEDONS 
ii. THE EVOLUTION OF THE SIEVE-TUBE 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 169 
ANSEL F. HEMENWAY 
(WITH PLATE XI AND THREE FIGURES) 
In 1909-10 the writer studied the phloem of some 30 species 
of lower dicotyledonous trees and found that the sieve-tubes in 
these species had the same general structure as those of the gym- 
nosperms or vascular cryptogams.t Some 60 species of higher 
woody dicotyledons were investigated the next year, and this 
last year about go species of herbaceous dicotyledons and 12 
monocotyledons have been studied. 
As the literature on the subject of phloem has been rather well 
reviewed and catalogued recently, an exhaustive review of it will 
not be given here. In 1908 Hirt? gave a good review of the 
literature from the histological standpoint. MANHAM® similarly 
discusses the literature from the physiological side. CHAUVEAUD‘ 
in an extensive paper gives a brief review of the literature of phloem. 
The material for this investigation was collected in late summer 
or early fall, the object being to get the sieve-tubes in mature 
condition, so that they would best show callus formation. For 
the sake of comparison, several species were studied in seedling 
condition and in the adult growing condition. 
Before proceeding to the discussion of the evolution of the 
sieve-tube, a few general observations on phloem anatomy may 
well be mentioned. The distribution of the hard bast in the woody 
MENWAY, ANSEL F., Studies on the phloem of the dicotyledons. I. Phloem 
of va Juglandaceae. Bor. Cx: 51:131-135. pl. 13. 191t. ‘ 
? Hitt, A. W., The histology of the sieve-tube of angiosperms. Ann. Botany 
22:245-290. pls. 17, 18. figs. 13. 1908. 
3 Manuaw, S., The conduction of carbohydrates. Science Prog. Oct. 1910 and 
Jan. 1grt. « 
4 CHavveavp, G. L., L’appareil conducteur des plantes vasculaires et les phases 
principales de son Gvohution. Ann. Sci. Nat. Bot. IX. 13:113-438. figs. 218. 1911. 
Botanical Gazette, vol. 55] [236 
