Scott .— The Structure of Mesoxylon multirame . 
451 
figured (Text-fig. i) there are three areas on the radial wall of a tapering 
element, which show little bright dots on a light-brown background, and 
appear clearly to be lateral sieve-plates. Further, in a tangential section, 
the long oblique wall between two such elements shows, in sectional view, 
a number of thin places marked out in brown, which are no doubt the 
sections of sieve-plates or fields (Text-fig. 2). 
In the outer part of the phloem the parenchyma consists of shorter and 
wider cells than elsewhere, reaching 60 [x 
in diameter, with a length of 170-48 /x 
(PI. XII, Figs. 9 and 10). In the same 
region, elements have been observed 
with a thick spiral band ; whether they 
were sieve-tubes or not cannot be as¬ 
certained. There was evidently some 
thickening or deposit on the walls, 
which became drawn out during growth 
into a spiral form ; similar cases have 
been observed in the phloem of recent 
Ferns. 
We may distinguish, then, three 
kinds of elements in the phloem—the 
long, perhaps resiniferous tubes, the 
sieve-tubes, and the phloem-paren¬ 
chyma. There remain the phloem- 
rays. In the outer part of their course 
they are appreciably dilated—2-3 cells 
wide, with the cells themselves much 
enlarged (PI. XII, Fig. 9). They some¬ 
times have brown contents, like those of 
the long tubes. Where the phloem abuts 
on the pericycle, much broader rays are 
often met with; these are probably 
principal rays, lying between the groups 
of primary phloem. The latter are 
difficult to recognize in transverse section. A slight bulge in the outer 
margin of the phloem can sometimes be recognized opposite a primary 
xylem-strand, and occasionally a little group or band of rather thick-walled 
elements is seen in this position, perhaps representing the altered sieve- 
tubes of the primary phloem. 
The general structure of the phloem of Mesoxyton multirame agrees 
very nearly with that of M. Sutcliffii , as described by Mr. Maslen (Maslen, 
1911 , p. 400). The phloem of M. Lomaxii and M.poroxyloides is evidently 
very similar, though the preservation in the observed specimens is not so 
Text-fig. 2. From a tangential section 
of the phloem, showing sieve-tubes, paren¬ 
chyma, and rays, s.p-s.fi., wall of a sieve- 
tube, showing numerous sieve-plates in 
section, x about 150. R. S. S. 2773. 
