548 Brebner. — On the Anatomy of 
the older and more recent conceptions of the morphological 
importance of certain histological layers are being abandoned. 
Farmer and Hill point this out with regard to the endodermis 
and histogenetic layers, and Pitard 1 expresses himself as 
follows with regard to the pericycle : c Cette notion du peri- 
cycle apparait done en definitive comme inadequate aux faits 
et sans utilite pour l’expression.’ The writer is quite in accord 
with these views, and thinks these layers should be, in many 
cases, abandoned as morphological criteria. 
The new terms put forward tentatively have been based 
almost entirely on the idea of the stele as originally set forth 
by Van Tieghem. In view of the writer’s belief in the 
unimportance of the endodermis, pericycle, &c. as morpho- 
logical criteria, it is somewhat doubtful if the method adopted 
was a wise one. It would perhaps have been better to 
abandon the stelar theory altogether, and substitute for it 
the conception of a connected system of vascular strands on 
the one hand and non-vascular tissue on the other. At the 
same time the non-vascular tissue would not be considered as 
something essentially and fundamentally different from the 
vascular, for they are both differentiated from the same 
meristem, and what has become vascular in one case might 
very well be non-vascular in another or vice versa. To take 
one illustration : in most Dicotyledons the pith is simple with 
no vascular strands, but in some cases there are what are 
called ‘ medullary bundles.’ Therefore the pith in Dicotyle- 
dons may be said to be potentially vascular. It is undesirable 
to apply the term stele to the suggested conception of the 
vascular system, but perhaps another and suitable term may 
be found which could be combined with the prefixes already 
used to distinguish the different stelar systems. They could 
further be appropriately dealt with as follows :■ — The vascular 
system of typical Dicotyledons would be described as cyclo - 
desmic , Monocotyledons as atactodesmic , the vascular network 
of Ferns as dictyodesmic , and so on. These terms might even 
1 Pitard, * Le pericycle et la taxonomie : valeur anatomique du pericycle,’ Actes 
de la Societe Linneenne de Bordeaux, s 6 r. vi, t. vi, 1901, p. 43-61). 
