Physiological Studies in Plant Anatomy 33 
showing the same type of etiolation has fully confirmed the correctness 
of this line of thought. The stem of the etiolated broad bean seedling 
possesses a fully developed functional endodermis from its base to 
close behind the growing apex. On the other hand, in Phaseolus 
Multiflorus, the apex of the etiolated plant is readily penetrated 
throughout by an acid dye when driven in under pressure, the 
plumular hook does not persist so long, the leaves open much more 
widely, though yellow in colour, and both etiolated hypocotyl and 
epicotyl of the epigeal seedling are free from any trace of a primary 
endodermis. 
As is pointed out later, the presence of such an endodermis in 
some etiolated stems has been noted previously, but its significance 
has remained unnoted and in most cases its presence has not even 
been detected. Hand sections cleared in boiling potash or Eau de 
Javelle, and then stained with safranin, gentian violet or other basic 
stains, show the endodermis very clearly. Sections stained in 
phloroglucin and mounted in strong hydrochloric acid demonstrate 
it clearly without clearing, as the contracted protoplasm invariably 
stretches tangentially across the cell, remaining firmly attached to 
the Casparian strip. In any case of doubt certainty may be obtained 
by carefully macerating a fresh section in concentrated sulphuric 
acid, when the Casparian strip persists as a characteristic network 
(Priestley and North ( 17 )). 
On the other hand, in some stems, such as Phaseolus multiflorus , 
which do not show such striking etiolation phenomena, the apical 
development, even in darkness, pursues another course and no 
functional endodermis appears in either the etiolated or the normal 
stem. Earlier papers in this series (Priestley and North ( 17 ) and 
Priestley and Woffenden(i 9 )) have demonstrated that the presence 
of an endodermis has considerable influence upon the further struc¬ 
tural development of the organs in which it develops. It now remains 
to show that the main structural features connected with etiolation 
phenomena such as shown by the broad bean may be associated 
with the presence of this endodermis. 
In the first place this endodermis restricts the nutrient sap neces¬ 
sary for growth to the tissues within the endodermis and to the apex. 
We have here a natural cause of the excessive elongation of the stem, 
as the only meristem cells receiving adequate supplies of food for 
growth are those at the base of the apical meristem which caps the 
end of the endodermal cylinder. Growth of this meristem adds to 
the length of the stem, and growth in length is therefore favoured at 
Phyt. XXII. I. 
3 
