348 
L. H. MACDANIELS 
newed emphasis on the value of anatomy in taxonomy, maintaining 
that internal morphology should be given weighty consideration in 
working out phylogenetic relationships. Thus, mainly upon anatomi- 
cal characters, the division of vascular plants into two great groups, 
the Lycopsida and the Pteropsida, has been made. In these papers 
Jeffrey has also put forth and strongly emphasized the importance in 
plants of the principle of recapitulation based on the fact that the 
seedling in its ontogeny often recapitulates ancestral characters. 
Hence, by the study of sporelings of pteridophytes and seedHngs of 
angiosperms, stelar types in these groups and the probable evolution 
of the stele have been determined. 
In addition to types of stele, various other characters have also 
been given weight in classification. Among these may be mentioned 
types of vessel and the distribution of parenchyma in xylem. It is 
held by the last-named author and others (6) that vessels with scalari- 
form end walls are primitive, whereas those with porous ends are ad- 
vanced. In the same way, the terminal position of the wood paren- 
chyma is considered most primitive, the vasicentric position most 
advanced, and the diffuse position intermediate (9). 
Phylogenetic significance was first assigned to types of sieve tubes 
found in angiosperms by A. F. Hemenway in two papers entitled 
"Studies on the Phloem of the Dicotyledons" (191 1, IQ13). In the 
first of these, covering six species of the Juglandaceae, the point is 
made that the sieve tubes of that family have well-developed sieve 
plates upon the side walls which do not differ from those on the end 
walls. Such a condition resembles that found in the gymnosperms 
and vascular cryptogams; hence the phloem of the Juglandaceae is 
primitive, and its sieve tubes represent the type primitive among 
angiosperms. 
In Hemenway 's second paper, after the study of ninety-six species of 
woody dicotyledons belonging to seventy-five genera and enough herb- 
aceous monocotyledons and dicotyledons to make the total number of 
genera studied one hundred and forty, the following points are made: 
The forms studied are grouped under three principal types which 
are indicated in text-figures 1-3, after Hemenway 's figures. 
The first type, according to that author, resembles the sieve tube 
of Pinus, with the sieve plates on the side wall identical with those on 
the end wall. The terminal wall in this case is very oblique, extending 
from one fourth to one half the length of the sieve tube element. 
