288 Scott and Brebner . — On Internal Phloem 
second node below. The internal phloem accompanies the 
leaf-trace bundles into the stem, and runs straight down 
through two internodes, where it joins that of the next bundle 
vertically beneath. It is usually at this point that branches 
arise which penetrate somewhat more deeply into the pith, 
while those which reach the middle of the stem are given off 
lower down still. Hence as a rule the transverse section of 
the youngest internodes shows a single ring of internal 
phloem-groups, a rather older part has a double ring, while 
the more central groups arise by the division of pith-cells at a 
comparatively late stage. But there is no great constancy 
about this and occasionally the more internal branches arise 
much earlier. The different strands are further connected by 
anastomoses 1 . We may add that sometimes phloem-groups 
are formed outside the protoxylem elements, between these 
and the rest of the wood. This is an approach to the forma- 
tion of interxylary phloem-islands, as in some other Gentians, 
Chironia , &c. 
We have described the distribution of the phloem in this 
plant because it shows an extreme modification of ordinary 
bicollateral structure, and yet is readily referable to the type. 
It may be added that the external phloem-groups are also 
very scattered and widely separated from the xylem, so that 
there is a certain analogy between the two systems as regards 
distribution. We pass over our other observations on plants 
with strictly bicollateral bundles, as they present no new 
points of importance, and go on to a plant the remarkable 
structure of which is only indirectly connected with our main 
subject. 
5. Acantholimon glumaceum , Boiss. (Plumbagineae). The 
anatomy of this genus has already been the subject of several 
investigations, the earliest of which is due to Prof. Oliver 2 , who 
especially insists upon the absence of typical medullary rays. 
He also observed and figured among other peculiarities the 
1 Cf. Meyer, loc. cit., p. 502 ; and Jost, loc. cit., p. 439. 
2 D. Oliver, On the structure of the stem in certain species of Caryophylleae 
and Plumbagineae ; Trans. Linnean Soc. vol. XXII, 1859. 
