in the Genus Primula. 
3*9 
seedling and also in the mature plant of P.japonica (cf. Van 
Tieghem, 1 . c., No. 24, p. 483). 
From one point of view the chief peculiarities of this type 
of structure may at the same time be epitomized and explained 
by considering that the leaf-trace, when it enters into the 
circle of vascular tissues, carries the endodermis of its upper 
surface straight in with it through the breadth of the vascular 
ring, where this endodermis then turns down at the inner 
border of the trace and runs down the stem, spreading laterally 
at the same time so as to form the internal endodermis of the 
vascular ring or stele, as the case may be (Fig. 10). 
In P. involua'ata the epicotyledonary central cylinder is 
maintained until the seventh leaf, or even higher. The first 
two or three leaf-traces, including those of the cotyledons, 
produce a gap of about two or three cells wide, the higher 
ones of about six cells. In the latter the endodermis, in passing 
over the gap, becomes slightly concave ; however, this infolding 
is not deep, and the endodermis soon straightens out again 
as the gap fills up (Fig. 11). When the seventh or eighth 
leaf-trace comes off, this infolding of the endodermis is carried 
on to a much greater extent, and at the same time the gap 
remains open for an unusually long distance ; so long, indeed, 
that the next leaf-trace above is given off from the opposite 
side of the stem before it becomes closed (Fig. 12). Around 
the margins of this gap also the endodermis is very deeply 
infolded, so much so, in fact, that it meets and fuses with the 
endodermis infolded from the other side through the still 
unclosed gap of the seventh or eighth leaf-trace (Fig. 13). 
Later on they separate completely, thus dividing the vascular 
ring into two separate groups, each completely surrounded by 
its own endodermis and forming an incomplete stele or gamo- 
desmic group. Proceeding upwards, these fuse across the 
earlier gap left by the seventh or eighth leaf-trace, to form 
a horseshoe-like group which remains open on the opposite 
side of the stem (eighth or ninth leaf-gap) until the next 
leaf-trace above comes off (Fig. 14), which divides it in an 
exactly similar manner into two new groups, and so on. 
