THE HISTOLOGY OF THE PHLOEM IN CERTAIN WOODY 
ANGIOSPERMS^ 
L. H. MacDaniels 
The study of phloem as a distinct tissue with an important and 
speciaHzed function may be said to have begun in 1837, when Theodor 
Hartig discovered the sieve tube and announced that the sieve plates 
are perforated. This discovery, important as it was, apparently re- 
ceived little recognition for nearly twenty years, when Hartig's ob- 
servations were confirmed and extended by Von Mohl (1855), Schacht 
(i860), NageH (1861), Hanstein (1865), and Dippel (1869). The 
work of these men, together with that of De Bary, established the fact 
of the universal occurrence of the sieve tube in the angiosperms, and 
of very similar structures in the gymnosperms and the vascular cryp- 
togams. 
The work of the last-named author is particularly significant in 
that, in addition to his own research, the work of previous investi- 
gators was brought together and organized and a nomenclature estab- 
lished which, for the most part, is still in use. Since the work of 
De Bary, numerous investigations on phloem have been published. 
From the physiological point of view the work of Fischer (1884), 
Haberlandt (1884), Czapek (1897), and others stands out as important; 
from the standpoint of histology, probably the most significant pub- 
lications are those of Wilhelm (1880), Janczewski (1882), Russow 
(1883), Lecomte (1889), Poirault (1893), Perrot (1899), Strasburger 
(1901), and two papers by A. W. Hill (1901, 1908). These papers 
vary much in nature, but are concerned chiefly with the development 
and structure of the phloem of mature stems. The idea of relating 
anatomy and histology to taxonomy and phylogeny by the methods 
follow^ed by Schwendener and Solereder, and, in a broader and more 
fundamental way, by Williamson and other workers in paleobotany, 
had not been applied to the phloem by any of these investigators. 
The papers of Jeffrey, however, in 1900 (11) and 1902 (12), laid re- 
^ Contribution from the Department of Botany, College of Agriculture, Cornell 
University. 
347 
