The Chicago University Text-Book. 
353 
astelic angiosperms “ without organisation into a definite cylinder,” 
but is perforated by gaps having a considerable, but not an un¬ 
limited, variability in size and position. 
It is scarcely correct to say that “ all of the four kinds of 
bundle (? stele) described above as occurring among ferns are 
prevailingly mesarch.” In a very large number of cases, probably 
the majority, the steles of ferns are endarch, i.e., the protoxylems 
are developed on the inner limit of the xylem. 
The paragraph about the relation of apogamy and apospory 
to the number of chromosomes (p. 170) should, we think, have been 
elaborated. Some indication of the fact that apospory and 
apogamy are often associated in the same life-history, and of what 
happens to the number of chromosomes in such cases, is surely 
required. 
It seems a mistake to illustrate the structure of the apical 
meristem of angiosperms by a figure of Hippuris, which has been 
shown to represent a rare condition of the layered meristem. 
The term “dotted ducts” (p. 241) is surely an obsolete and 
unnecessary synonym for pitted vessels; and why should the 
tracheids of pteridophytes be “ known as scalariform vessels ” ? 
On p. 243 it is said that the vascular system of the mature stem 
of dicotyledons “consists of a hollow cylinder composed of vascular 
bundles and inclosing the pith (a siphonostele). Traversing the 
vascular cylinder from the pith to the cortex, and hence separating 
the bundles, are the pith rays.” The second sentence ignores the 
pericycle, and regards the bundles of a typical dicotyledon as 
isolated strands running through ground tissue, separated topo¬ 
graphically into cortex, pith and “ pith rays.” This position, 
if it is really intended, seems to take us back to the days before the 
doctrine of the stele was established. The term “ pith-ray ” or 
“ medullary ray ” has become rather misleading as applied to the 
rays of the typical dicotyledon. If, however, the position be 
defended, it is inconsistent with calling the vascular system a 
“ siphonostele,” especially when we consider the description of the 
the vascular system of Pteris on p. 157 as already criticised. 
Surely it is an exaggeration to say (p. 245) that the ampin- 
vasal bundle is “ characteristic ” of the mature stems of mono¬ 
cotyledons. 
The description of secondary thickening of the vascular cylinder 
of a root (p. 248) is not quite satisfactory, nor does it quite tally with 
Figs. 556 and 557. There can be no “ primary pith rays” in a root 
