Seedling Structure of Gymnosperms. /. 703 
xylem groups, to bring the protoxylem into an exarch position, is very 
slow. The protoxylem lies buried in the centre of the metaxylem for 
some distance downwards, and the metaxylem elements slowly take up 
a more internal position; but this does not bring the protoxylem, which 
is gradually becoming less in amount, into the desired position, owing to 
the differentiation of new xylem elements outside it, which addition is 
much more marked than that described for Juniperus virginianum , 
Indeed, a careful study of these tracheae downwards towards the root 
apex, warrants the conclusion that in L. decurrens the protoxylems of 
the cotyledons die out and that new protoxylems are organized in ap 
exarch position, which means that the protoxylems of the root are not 
directly continuous with those of the seed-leaves. 
A similar state of affairs has been described in T orreya My r is tic a 1 , 
but at present it is not possible to state whether this occurrence is normal 
for ’ Lib ocedrus \ it is not unlikely that, bearing in mind the variations 
mentioned, the plant here described may be somewhat abnormal. 
Thuja sphaeroidea , Spreng. All the seedlings of this and of the 
other species examined had two cotyledons. The transition and other 
features resemble Juniperus virginianum in all respects. 
TJuja orientalis, Linn., Is almost indistinguishable from Th. sphaeroi - 
dea, the only difference noted being that in Th. orientalis the bifurcation of 
the phloem of the seed-leaf bundles begins directly the inward passage 
of the strands commence. 
Thija orientalis var. aurea and Th. japonica are essentially similar to 
Th. sphaeroidea. 
Actinostrobus pyramidalis , Miq. Owing to our failure in obtaining 
material, our observations on this plant are based upon some preparations 
made by the late Mr. Robertson Glasgow, and kindly placed at our 
disposal by Dr. D. H. Scott. 
ActinostrobiLS pyramidalis resembles TJmja orientalis ; the difference 
between them may be looked upon as one of degree rather than of 
kind. The bundles of the cotyledons, which are two in number, are single 
collateral structures throughout the whole length of each Seed-leaf, but 
directly the’ axis is entered each trace divides into two half-bundles, 
the division being in the cotyledonary plane. This bifurcation extends 
not merely through the phloem but also affects the metaxylem. Rotation 
takes place around the protoxylem, so that the latter tissue is practically 
in an exarch position as soon as the central region of the hypocotyl is 
reached (Diag. 6, Fig. 1), the metaxylem and phloem-masses being 
placed on either side. Fusion of the opposing groups of vascular elements, 
other than protoxylem, takes place, thus resulting in the formation of 
a diarch root (Diag. 6, Fig. 2). 
1 Chick, E., loc. cit. 
