7°8 
Thomas. — Seedling Anatomy of 
groups, &c., the xylem decreases in quantity until only the two small 
protoxylem strands remain. 
Berberidaceae. 
The genus Berberis is of great interest, inasmuch as both the tetrarch 
and the diarch condition are to be found within the genus, and even within 
the species, as in B. macrophylla. 
Berberis Lycium . The hypocotyl shows four diagonal strands of 
phloem with some metaxylem to the inside, and with obvious exarch 
protoxylem elements in the cotyledonary plane, and somewhat less obvious 
ones in the intercotyledonary plane. At the node the usual double strand 
passes out into the base of the cotyledon, and is continued up the petiole. 
J7 At the base of the hypocotyl the slight adjust- 
ments take place which convert the structure into 
that of a typical tetrarch root. (See PI. LI, Figs. 
21-6 of Althaea rosea.) 
B. aristata shows similar features, but may 
reduce to triarch, while B. macrophylla reduces 
rapidly to a triarch, and sometimes later to a diarch 
condition. 
B. vulgaris , B. aquifolium , B. nervosa , B. 
heteropoda show early fusion of the phloem groups 
and a diarch root. 
Comparison of seedlings at different stages in 
these species shows very clearly the changes pro- 
duced by age. Thus in B. aquifolium , at an age 
when the first leaf is just visible, the halves of the 
double bundle appear to be very widely separated 
at the cotyledonary node on account of the 
obliteration of the central protoxylem group and 
the semi-obliteration of the two tangentially produced wings, while inside 
the four phloem groups are to be found masses of metaxylem not to 
be found at an earlier age. 
Podophyllum Emodi. This species has a very long cotyledonary tube 
with a small central cavity, which becomes occluded in the upper part and 
widens out round the plumule near the base. The root is typically diarch, 
but the plate in the hypocotyledonary region develops intercotyledonary 
xylem arms between the phloem groups, which produce a tetrarch appear- 
ance reminiscent of the tetrarch species of Berberis. These groups are 
continued upwards into the plumular leaves, and the main strands are con- 
tinuous above with the double bundles of the cotyledons in the usual 
manner. The double bundles are remarkable for the extremely exarch 
position of the xylem, which constitutes the apex of an outwardly directed V 
18 
Text-figs. 16-18. 16, 
Berberis Lycium ; 17, B. aris- 
tata ; 18, B. vulgaris. All § 
nat. size. 
