38 J. H. Priestley and J. Ewing 
in size consequent upon vacuolation. These results point to the 
inability of the nutrient sap to reach the leaf meristem, such an in¬ 
ability as is suggested by the observations and experiments described 
in the previous section, and it depends in all probability upon the 
nature of the wall between the protoplasts in the etiolated meristem. 
But if the leaf rudiment is exposed to light even for a short time, 
this characteristic of the etiolated wall disappears, the nutrient sap 
readily penetrates the meristem and subsequent development of this 
leaf is possible even if the leaf is retained in darkness. There is there¬ 
fore no essential contradiction in the different results reported by 
the observers quoted above. 
The undeveloped leaf rudiments of the broad bean or other plant 
of this type when etiolated should therefore consist of dense protein- 
filled protoplasts with little water or inorganic salt present because 
they are cut off from the sap rising from the roots. Such chemical 
data as are available seem to support this conclusion and emphasize 
the difference between this leaf type under etiolation and the Mono¬ 
cotyledon leaf with basal growth. Thus in Vicia Faha L. the water 
content of etiolated leaves is lower than that of young green leaves 
(Palladin(ii)), while Karsten(8) has shown that etiolated leaves of 
Phaseolus, and Godlewski(6) that etiolated leaves of Raphanus con¬ 
tain less water than the green leaves. Palladin(i2) gives the following 
figures for percentage protein content in fresh weight: broad bean, 
green leaves 4*95, etiolated 8-38; wheat, green 1-99, etiolated 1-28. 
He also finds no soluble carbohydrate in the etiolated leaves of the 
broad bean, whilst in wheat he finds an amount equivalent to 2*67 
per cent, of the fresh weight. Weber ( 25 ) shows that etiolated leaves 
contain a lower percentage of ash than normal green leaves, being 
especially deficient in calcium. 
The Etiolated Stem 
Sachs(22) again creates two categories: (1) stems which usually 
develop within the sheath of enveloping tissues, and which in con¬ 
tinued darkness extend in length still more; (2) stems normally de¬ 
veloping in the light on which darkness produces little or no effect. 
Thus epigeal seedlings are less affected by growth in darkness than 
hypogeal seedlings, and seedling shoots are usually much more 
affected by growth in darkness than shoots from tubers (e.g. Dios- 
cored). The broad bean falls in Sachs’ first category, and many 
attempts have been made to explain the remarkable elongation re¬ 
sulting from growth in darkness. Kraus ( 9 ) thought that elongation 
