58 Scott and Brebner . — On the Secondary 
to a much greater length than their neighbours. They remain 
uninucleate. Several stages were observed between the ordinary 
desmogen-cell and the fully formed tracheide. The course of 
the tracheides, however, renders it impossible to trace them far 
in sections. Hence recourse was had to maceration, and 
Fig. 16 represents a couple of very young tracheides, one 
isolated, the other still in connection with some desmogen- 
cells, which were obtained by this method. The process of 
development is undoubtedly the same here as in Yucca and 
Dracaena. In Fig. 17, the whole length of a mature tracheide 
is shown, in two halves. It can be compared with the des- 
mogen-cells and young tracheides in Fig. 1 6, which are shown 
on double the scale of Fig. 17. 
The sliding-growth begins very early, and has already made 
considerable progress in the proximal half of the xylem, while 
cell-divisions are still going on in its distal portion. 
4. The Roots . — We found no secondary thickening in the 
adventitious roots at our disposal. From our experience in 
Dracaena , we paid special attention to the points of insertion 
of rootlets, but here also no signs of cambium were present. 
In fact, we may say for certain that the roots examined by us 
never could have formed a secondary zone. The whole of the 
cortex was already dying away, and the wide pericycle (8-10 
layers in thickness) was too sclerotic ever to become the seat 
of a secondary meristem. The roots are of polyarch structure, 
and call for no detailed description. It may be mentioned, 
however, that they contain true vessels of large size, whereas 
vessels, with the possible exception of protoxylem-elements, 
are altogether absent from the other organs of the plant. The 
larger vessels of the root may be either reticulated or have 
bordered pits. They have inclined scalariform terminal walls ; 
we demonstrated their perforation by injection with French 
Blue under pressure. 
This occurrence of large vessels in the root only is also 
characteristic of Dracaena. 
5 . Summary . — Our chief results respecting Arts tea are the 
following : — - 
