32 
J. H. Priestley and J. Ewing 
growing under conditions more normal to the root. In the case of the 
broad bean the apical meristem evidently remains in the same con¬ 
dition in which it was withdrawn from between the cotyledons, the 
plumular hook and its attendant leaf initials almost completely 
failing to grow, whilst the tissues of the stems are formed by the 
activity of the basal cells of the meristem situated below the curved 
apex. This lack of growth by the upper and more superficial cells of 
the meristem suggests that the nutrient sap supplied from the coty¬ 
ledons is percolating among the protoplasts of the meristem only 
with difficulty, and experiment supports this assumption. If an acid 
dye such as acid green is driven into the top node of these etiolated 
shoots under pressure, a pressure greater than one atmosphere, main¬ 
tained for twenty-four hours, fails to drive the dye into the meristem 
of the growing points, and the meristem cells above the termination 
of the vascular strand remain quite unstained. On the other hand, 
in the course of a few hours a pressure of half an atmosphere drives 
the dye through the apex of a green shoot grown in the light, when 
applied under the same conditions, and the meristem cells are soon 
deeply stained right out to the surface. 
The difficulty with which the nutrient sap penetrated the apical 
meristem of the root was attributed to the different composition of 
the cell walls intervening between the dense protoplasts of the meri¬ 
stem, and a similar cause is probably operating in the etiolated stem 
apex. In the root this different composition of the meristem wall was 
always associated with a characteristic anatomical feature. Imme¬ 
diately behind the growing apex a cylinder of cells differentiates 
from the meristem into a “primary endodermis” with Casparian 
strip (Priestley and North( 17 )). This early differentiation of a func¬ 
tional endodermis undoubtedly plays an important part in the future 
development of the root, and its own development seems to be 
causally connected with the nature of the apical meristem, although 
the chain of causation has not yet been fully traced. In the normal 
Angiosperm stem on the other hand when growing in the light a 
functional endodermis with Casparian strip is usually not present, 
its place being taken by the “starch sheath.” If, therefore, the stem 
apex of the broad bean, when growing in continued darkness, is cor¬ 
rectly described as developing more like a root apex, it might be 
anticipated that the etiolated stem would contain close behind its 
growing apex a functional endodermis. Perhaps the most interesting 
point to record in the present paper is that an anatomical investi¬ 
gation of the etiolated stem of the broad bean and of other plants 
