Notes . 
185 
average size. In longitudinal sections it may be observed that sieve- 
areas are quite numerous on the vertical .walls of the tubes; these 
areas are especially well seen in those elements just external to the 
cambium, on account of the development of callus. 
Sclerenchyma is formed at a short distance from the cambium. 
The elements of this hard bast are aggregated into masses which 
are somewhat regularly arranged in concentric rings, each being 
interrupted by the medullary rays. Alternating with these broken 
circles of sclerenchyma are soft bast elements which gradually become 
less in amount as the outer zone of wood is reached, so that in the 
peripheral parts of the anomalous rings of bast the sclerenchymatous 
bands may be separated one from the other apparently only by a 
thickness of one or two parenchyma-cells. 
The individual elements of the hard bast do not call for much 
attention, inasmuch as they present the characters usually associated 
with such cells. Suffice it to say that they have very hard lignified 
walls with simple pits and, generally speaking, a very small lumen. 
For the sake of completeness it will be well to give a short description 
of the xylem. The wood is made up of the usual elements ; that is 
to say, vessels, fibres, and parenchyma. The vessels vary much 
in diameter ; in transverse section they are generally oval in shape. 
Very frequently the transverse walls of the original tracheides persist 
to a greater or less extent, in which case the remnant of the septum 
is much pitted. Xylem- parenchyma surrounds the vessels. The 
parenchymatous elements and the fibres are arranged in a somewhat 
regular manner in alternating zones. The cells constituting both 
these tissues have fairly thick lignified walls, those of the fibres being 
thicker than those of the parenchyma, and having simple pits. 
The medullary rays are narrow, generally from one to four cells 
in breadth. They are numerous, and the elements constituting them 
are simply pitted. From the nature of the material — a dried piece 
of old stem — it was impossible, unfortunately, to determine the 
exact mode of origin of the anomaly described above. It appears 
very probable however that it arises in a manner analogous to that 
of the phloem-islands in Strychnos , for example ; that is to say, by 
the formation of successive cambium-rings. It is hoped to further 
investigate the origin of the phloem-zones when fresh material is 
obtained. 
It is not proposed to enter into theoretical considerations con- 
