Notes on Recent Literature. 
363 
Alnus and other Cupuliferae as well as to various other woody 
plants, and concludes that it is the influence of the leaf-trace on the 
secondary wood which brings about the aggregation of ray- 
parenchyma in the neighbourhood of the point at which the trace 
enters the cylinder. In the course of its passage through the 
secondary wood the trace exercises a disturbing effect on the tissues 
“ expressed by a diminution of the number of vessels and by the 
increase of storage tissue, particularly by the enlargement and 
multiplication of the rays.” In some cases this aggregation of ray- 
tissue is confined to the immediate vicinity of the leaf-trace ; in 
others (e.g., Alnus japonic a) it extends upwards, and especially for 
some distance below the point of exit of the trace, and in transverse 
section several compound rays may be seen belonging to the traces 
of several nodes situated at various levels above the plane of section. 
In the “live” (evergreen) oak ( Q . virginiana) a relatively 
primitive condition obtains, in which there is comparatively little 
parenchymatous tissue above and below the leaf-trace during the 
first few years of growth; but later on, as may be seen from tan¬ 
gential sections taken through the younger wood, a long compound 
ray stretches down below the trace. In transverse sections taken 
below the trace this ray is seen to begin at some distance from 
the pith. 
In the deciduous oaks broad ray-formation in relation to the 
leaf-traces has been carried much further. In the “white” oaks 
these rays are developed mainly in connexion with the lateral 
bundles of each leaf-trace, and there are generally ten of them to 
be seen on a transverse section of the secondarily thickened stem, 
one pair corresponding to each lobe of the primary five-lobed stele. 
In the mature twigs of the “red” oaks the tendency to form 
compound rays has become more firmly established and numerous 
broad rays are formed in the secondary wood in addition to those 
connected with the lateral leaf-traces. 
The explanation of the differences between evergreen and 
deciduous oaks put forward by Bailey is that the alternation of 
seasons related to the deciduous habit has necessitated the formation 
of much more storage-parenchyma than appears in the evergreen 
forms. 
The broad rays are stated by Bailey to exercise a marked re¬ 
tarding effect on the rate of growth in thickness of the stem in the 
tracts which they occupy, so that the external surface of the wood, 
as seen when the tree is barked, may show a fluted character, the 
furrows corresponding with the broad rays. In some cases (e.g., 
Carpinus caroliniana) this fluting extends to the surface of the 
twig itself. This is an interesting phenomenon, of which no 
explanation is offered by the author. Can it be due to the difference 
in the water supply to the cambium opposite the rays, as opposed 
to that available where tracheids abut on the cambium ? One would 
have supposed that the rate of production of new tissue by the 
cambium would depend rather on the supply of organic substance. 
In this connexion it would be of interest to know how far the evo¬ 
lution of the phloem rays follows a parallel course to the rays of the 
xylem. This subject is not referred to in any of the papers under 
review. 
Simultaneously with Bailey’s paper (3) on “ The Relation of the 
Leaf-Trace on the Formation of Compound Rays,” there appeared a 
very interesting paper by Fames (4) on “The Origin of the Herbaceous 
