240 Ingvar Jorgensen and Walter Stiles. 
A single strand from this passed outward into the petiole at 
each node, about the level at which the median leaf trace left the 
stele. Just above this level, two vascular strands from the central 
cylinder entered the bud. 
All the vascular strands present in the normal stem had their 
counter-parts in the abnormal specimen. That their position, with 
regard to the central stele should have been modified in connection 
with the changed direction of leaf insertion was to be expected. 
It was interesting to find, however, that this displacement was 
almost the only alteration from the normal stem structure, and that 
no really radical rearrangement of structure accompanied the marked 
deviation from the normal mode of development of the shoot. 
It is clear that in this example, the hereditary characters of 
the internal structure have escaped serious disturbance such as 
perhaps might have been looked for in a shoot so aberrant in 
external features. 
CARBON ASSIMILATION. 
A Review of Recent Work on the Pigments of the 
Green Leaf and the Processes connected with them. 
By Ingvar Jorgensen and Walter Stiles. 
Preface. 
I N regard to the fundamental problems with which we shall deal 
in these articles, a considerable quantity of work has been 
done in recent years, and a mass of fresh knowledge has been 
obtained. Much of the information thus afforded is not very easily 
accessible, and to those not actually engaged on work on the subject 
a considerable time is necessary to disentangle the essential facts 
from unessential details. 
We have thought therefore that a review of the recent 
literature of the subject, in which the character of the involved 
problems is indicated, would be of interest. 
Chapter I. 
Introduction : Fundamental Principles. 
The elements contained in the plant are such as are always 
present in ample quantity in air and soil, but in the plant they 
exist in compounds possessing greater energy than the simpler 
substances in the surroundings. 
