Physiological Studies in Plant Anatomy 31 
teristic growth phenomena usually included under the phrase “ etiola¬ 
tion ” effects are obtained. In the case of the root meristem, by the 
method described in an earlier paper (Priestley and Tupper-Carey(i8)), 
its development in light and relatively dry air is readily secured, but 
the resultant structural changes are usually not great. In the case of 
Vida Faba L., two seem worthy of note in connection with the sub¬ 
sequent discussion: (1) the primary endodermis appears sometimes 
to be slightly later in developing opposite the xylem, as the Cas- 
parian strip is frequently formed opposite the phloem before it can 
be seen opposite the xylem; (2) small tubercles were frequently noted 
close behind the growing apex, but their development never pro¬ 
ceeded far, and the tissue of the tubercles never rose more than one 
millimetre above the surface of the root. 
The Experimental Study of Etiolation 
The discussion in the next section makes it very clear that an 
understanding of the causal factors at work in producing the struc¬ 
tural changes observed in etiolated plants has been much hindered 
by the very varied nature of etiolation effects in different plants. 
The discussion therefore in this section will be limited to the very 
characteristic type of reaction under etiolation conditions provided 
by a large number of plants of which the broad bean, Vida Faba L., 
or the potato, Solanum tuberosum L., may be selected as typical. 
Here the comparison will not be with other types of etiolation effects, 
but mainly with the normal green plant, and to some extent with 
plants not so markedly affected by etiolation conditions such as the 
scarlet runner, Phaseolus Multiflorus Willd. 
In the broad bean and potato the obvious effects of growth of the 
stem in continued darkness may be summarised as follows: the stems 
become greatly elongated and lose their angular or winged outline, 
being round or oval instead: the leaves are very little developed and 
remain yellow in colour: the stem apex narrows very suddenly upon 
the turgid stem, giving it a pinched appearance: in the broad bean 
the plumular hook of the embryo persists during growth. The stems 
are extremely rigid and are obviously turgid with sap, bleeding freely 
when cut across. Structurally xylem and sderenchyma are not de¬ 
veloped to such a marked extent as in the green plant, and a hollow 
pith is absent or late in development. 
These facts looked at from the standpoint of a former paper 
(Priestley and Tupper-Carey(i8) suggest a tendency on the part of 
the shoot meristem to behave more like a root meristem when 
