322 
Hill and de Fraine.—On the 
The cambium does not form, as far as has been seen, any phloem, 
so that the appearance is not altogether that of normal secondary thicken¬ 
ing (PL XXII, Figs. 2 and 3). 
It is in this region that the 
plumular strands effect a junc¬ 
tion with the cotyledonary traces, 
and the short tracheides are 
formed before the epicotyle- 
donary bundles are differen¬ 
tiated. In older seedlings, with 
the plumular vascular tissue 
developed, these tracheides be¬ 
come more abundant, their 
position is on the inner side of 
the protoxylem, and they serve 
as a bridge for the insertion of 
the epicotyledonary strands. 
A similar transverse girdle of 
tracheides occurs at an early 
stage in the nodes of the shoot 
and joins the two leaf-trace 
bundles together. 1 
This tissue may be looked 
Diagram 2. upon as a special development, 
differentiated in order that the 
means of communication between the different traces may be rendered 
more efficient. The accompanying figure, Diagram 2, illustrates the 
course of the bundles on one side : c. 1 and c. 3 represent seed-leaf- 
traces ; p. /, p. 2, . . . indicate the plumular strands; C. is the cotyledonary 
tube; P, y the epicotyledonary axis; and t.t. y the region of the special 
tracheides referred to above. 
Welwitschia. 
Welwitschia mirabilis , Hook. f. The morphology and structure of 
the seedlings of this plant have been fully described by Bower, 2 whose 
account we are able to corroborate in all essential features ; but, for the sake 
of completeness, it is desirable to draw attention to the more important 
facts bearing directly on the present work. 
The seedling is illustrated in Plate XXIII, Figs. 9,10, and 11, from which 
it may be seen that the epigeal cotyledons are two in number and relatively 
1 Strasburger, loc. cit. 
3 Bower: On the Germination and Histology of Welwitschia mirabilis (Q.J.M.S., xxi, 1881). 
