440 MR. W. C. WORSDELL ON THE 
seen; it must take place very high up, immediately below the 
insertion of the cotyledons. 
In the larger seedling, in the region close beneath the insertion 
of the cotyledons, viz. in the upper hypocotyl, there is an oval 
cylinder of well-developed secondary xylem and phloem enclosing 
a parenchymatous tissue in which is the diarch plate of xylem 
with its protoxylem group at each end, though this latter is be- 
coming broken up and the pith smaller in area in the uppermost 
part of this region. In the phloem, especially in the well-marked 
primary phloem, are numerous fibres, somewhat resembling 
tracheides as seen in transverse section. Outside this is a zone, 
several layers thick, of pericycle, bordered externally by a well- 
marked endodermis. In the pericycle of this region of the root 
concentric strands occur which, to the number of three or four, 
and varying in size and development, occupy isolated positions 
around the central cylinder. They are conspicuous and well- 
developed. Their central portion is filled with scattered, is0- 
diametric tracheides with reticulate thickenings, which are formed 
by a surrounding cambial layer; the latest-formed xylem- 
elements on the periphery of these are rather more regular in 
shape and position; phloem surrounds the whole, thus com- 
pleting the stele (fig. 5). Lower down in the hypocotyl it 1s 
seen how these structures originate. A cambium arises in the 
pericycle, forming phloem on the inside towards the central 
cylinder, and xylem on the outside. In some places, at the end 
of the central cylinder, the extrafascicular cambium is seen to 
be continuous with the normal cambium of the central cylinder. 
Gradually passing into the upper hypocotyledonary region, this 
anomalous cambium extends round and forms eventually the 
concentrie strands. This is evidently the same phenomenon as 
that described by Gregg in the root of Cycas Seemanni, Al. 
Braun *, although in my seedling the cambium has the form 
of a local ring, and never forms a zone round the centra 
cylinder. DEM 
In a younger part of the root, where secondary thickening 9' 
the central cylinder has, however, begun, there is as yet no trace 
of the extrafascicular cambium. -orch 
The youngest part of the root of the larger seedling 8 uM 
each group of protoxylem being forked, with diversin8 ps 
An outer periderm of three or four layers is present. 
* * Annals of Botany,’ vol. i. 1887. 
