154 Scott. — On some recent progress in' our 
In the tissue lying outside the bundles already developed. 
Until quite recently it has been supposed that these anoma- 
lous cambial layers differ essentially from normal cambium 
in the fact that the bundles which they form are produced 
In their entirety on the inside of the meristematic zone, the 
development of all their elements being thus centrifugal. 
This is the view of de Bary and van Tieghem, the former of 
whom speaks of the phloem in all these cases, on account of 
its supposed centrifugal development, as forming part of the 
wood. 
The investigations of Mo rot and Herail (1885), with 
which many independent observations of my own agree, have 
shown that this view is wholly incorrect. Extrafascicular 
cambium acts precisely like normal cambium, producing 
wood internally and phloem externally. In those cases 
where the same zone appears to be permanently active it 
is really completed after the formation of each bundle by 
the appearance of a new cambial arc outside each new 
phloem group. Hence there is no need for the paradoxical 
terminology formerly used, and these cases are rendered more 
easily comparable with normal development. The analogy 
with such Monocotyledons as Dracaena probably led the 
earlier observers wrong ; in these latter cases the process is 
essentially different from dicotyledonous thickening, as the 
entire bundles arise inside the so-called cambium. In 
Strychnos again, as has been shown by Herail and by myself 
and Mr. Brebner, the remarkable phloem-islands are formed 
like normal phloem centripetally outside the cambium, and 
subsequently become enclosed in the wood by means of a 
new cambial arc completing the normal zone. 
Phloem-islands imbedded in the wood are now known to 
occur in at least twenty-four genera belonging to ten natural 
orders. In some of these, as in Salvador a, the development 
appears to be really centrifugal. In the great majority of 
cases, however, whether normal or anomalous, cambium pro- 
duces wood only on one side, bast only on the other. 
Many anomalies of structure in Dicotyledons have been 
