364 Notes on Recent Literature. 
Type in the Angiosperms.” The author points to the fact that no un¬ 
doubted herbaceous types of vascular plants are known from the 
older rocks: to the herbaceous character of the modern represen¬ 
tatives of the great arborescent Pteridophytic stocks which 
flourished during later Palaeozoic times: to the arborescent 
character of practically all Gymnosperms: to the preponderance of 
herbaceous forms among the derived groups of Angiosperms, e.g., 
the Monocotyledons and the higher Sympetalae: and concludes that 
there is a great deal of evidence tending to show that arboreal 
forms are relatively primitive and herbaceous forms derived. He 
then proceeds to enquire as to the factor which has led to the 
production of the typical anatomical structure of the herbaceous 
stem from that of the woody plant. He finds this factor in the 
influence of the leaf-trace. The extension of parenchyma from the 
neighbourhood of the node in vertical radial bands forming broad 
rays, as described by Bailey, eventually dissects the woody cylinder 
into wedges. The cambium at first extends across the broad rays 
and produces “ inter-fascicular tissue,” but in a later stage of the 
progression is restricted to the bundles themselves, and ultimately 
(as in Monocotyledons) dies out even in them. Certain genera of 
Rosaceae with persistent woody underground rhizomes and herba¬ 
ceous aerial stems were found to be very instructive in this con¬ 
nexion. The more or less woody rhizomes of several species of 
Potent ilia, for example, show broad alternating wedges of tracheids 
and parenchyma. Each parenchymatous band has, however, a 
small group of xylem on its medullary border, and these groups are 
found to be leaf-traces. If the wedges of secondary xylem were 
reduced in size a structure would be arrived at such as is found in 
many herbaceous forms. At the base of the aerial stems of various 
species a continuous woody cylinder occurs: as the stem is traced 
upwards, the leaf-traces are gradually isolated and the ring of 
bundles that eventually remains is composed of traces and “common ” 
bundles of the stem. Taken together with the fact that the epi- 
cotyledonary seedling stem of many herbaceous angiosperms has a 
continuous ring of primary xylem (as shown in several cases by 
Professor Jeffrey and others), which breaks up into distinct bundles as 
it is traced up into the later formed stem, such phenomena as these 
furnish a very good foundation for the belief that the typical stele 
of herbaceous plants with separate bundles showing little or no 
secondary thickening is essentially a derived type whose ancestors 
possessed a continuous primary xylem ring which underwent 
secondary thickening. 
Both Eames and Bailey point out that such a theory directly 
contradicts the view which would regard the herbaceous type as 
primitive, and secondary thickening as arising first in the bundles, 
and later by means of an “ inter-fascicular cambium ” extending 
between them and uniting the originally separate bundles into a woody 
cylinder. Though the facts have often been stated in such a way 
as to imply a theory of derivation of the woody from the herbaceous 
type we doubt whether such a view has been held, as a deliberate 
phylogenetic theory, at all so wudely as these authors believe. 
Bailey says that this conception originated with Sanio, was 
“ exploited” by Sachs and De Bary, and has been since adopted by 
subsequent “authoritative writers.” It is, perhaps, difficult for the 
younger workers of the present generation, who have always been 
used consciously to apply the method of comparison with a view to 
