STUDIES ON THE PHLOEM OF THE DICOTYLEDONS! 
I, PHLOEM OF THE JUGLANDACEAE 
ANSEL F. HEMENWAY 
(WITH PLATE XIII) 
During the past year the writer has studied the phloem of 
Juglans nigra, Juglans cinerea, Carya ovata (hickory nut), Carya 
alba (mocker nut), Carya glabra (pig nut), and Pterocarya caucasica 
(Caucausian walnut). The phloem of some thirty species of other 
lower dicotyledonous trees has also been investigated in a prelimi- 
nary way. Next year this research will be continued. A general 
account of the literature on the subject will be presented in the 
subsequent paper. 
The sieve tubes of the gymnosperms and the vascular crypto- 
gams have sieve plates on their lateral walls as well as on their 
fusiform end walls; while in the angiosperms true and typical 
sieve plates are supposed to be confined to the oblique or horizontal 
end walls of the sieve tube. 11? states: 
The term “‘sieve field,” in the sense in which it is used in this paper, denotes 
the group of fine connecting threads or strings which are found normally on the 
lateral walls, and which serve as a means of communication between adjoining 
sieve tubes. The sieve plates occur on the horizontal or oblique end walls of 
the sieve tubes, and occasionally on the lateral walls also, but their slime strings 
are readily distinguished from sieve fields owing to their large size. 
The object of the present research was to discover, if possible, 
any ancestral characters of the phloem, and especially to determine 
if the sieve tubes of any of the lower dicotyledons had lateral 
“sieve plates” instead of lateral ‘‘sieve fields.” 
In collecting material, it was found that the pieces of tissue 
from the main trunk of large trees were most satisfactory. Speci- 
mens taken from the trunk near the ground were texturally too 
‘Contributions from the Phanerogamic Laboratories of Harvard University, 
2. : 
* Hitt, T. G., Histology of sieve tubes of the angiosperms. Annals of Botany 
8 
22:265. 1908. 
131] (Botanical Gazette, vol. 51 
