SELBY: STUDIES IN ETIOLATION 69 
larger than in the normal, while the same gorging of the stems 
with starch grains was noted in the perimedullary region and in 
the medullary rays. The earlier formation of phellogen in the 
etiolated stem may be interpreted as an adaptation to prevent dry- 
ing out; this phellogen was present near the summit of the etio- 
lated stem. This precocious phellogen formation, in this case 
with the early collapse of the epidermis, is similar to that observed 
by MacDougal in Acer and Cornus.* 
Etiolated specimens with stems 50 to 60 cm. in length were 
brought into diffuse illumination near a window and in two months 
made an additional elongation of about 5cm. The terminal newly 
formed portions of such stems bore about 7 normal leaves, with 8 
or 10 internodes immediately below still retaining the bract-like 
organs resulting from etiolation (plate 4, figure 5). The lower 
portion of the stem, in which precocious development of phellogen 
had taken place, retained its brown color but was not extended, 
while the entire upper portion of the stem had become green. 
Young stems which had made but little growth in darkness made 
much more rapid growth than that described above for the older 
stems, and developed an equal crown of normal leaves. 
The leaves of the normal plant (plate 4, figure 6) showed a 
single layer of palisade-cells and no stomata on the upper surface, 
as before noted by Solereder.+ The petioles showed definite 
cambium, but the vessels gave no lignin reaction. The bract-like 
hairy leaves of the etiolated plant (plate 4, figures 3 and 4) showed 
no cambium in petioles, no stomata and no further differentiation 
of the tissues than an indistinct row of palisade cells, whose 
length and width were nearly equal. 
Rootstocks of Euphorbia corollata obtained from Ohio, were 
also grown in light and darkness under conditions similar to those 
for Persea. No essential difference in the rate of growth, or in 
the total amount of tissue produced, was observed as between the 
normal and the etiolated growths of Euphorbia (figures A and £). 
There was hoticeable variation in the thickening of the etiolated 
Stems due to an increase of cortex by activity of the cambium layer. 
* MacDovaat, D. T. The influence of light and darkness upon growth and 
Oieipebent (Mein, N.Y. Bot. Gad. =:).o}-200, 18KAGh | 100k 
SOLEREDER, H. Systematische Pflanzenanatomie 774. 1900. 
