40 
J. H. Priestley and J. Ewing 
McDougal(iO) has some very interesting observations which can 
probably be explained in the same way. In Apios Apios, Castanea 
dentata Marsh, Hicoria minima and H. ovata, Quercus palustre de Roi, 
and Q. rubra L., he reports a deep-seated periderm in the etiolated 
plants, whilst the normal stems possess superficial periderms. Un¬ 
fortunately McDougal did not make any close histological observa¬ 
tions so that it is left for subsequent investigators to see whether 
this deep-seated periderm in the etiolated plant arises within a func¬ 
tional endodermis. 
Further evidence of the restriction of growth activity to regions 
within the endodermal cylinder in this type of etiolated plant is pro¬ 
vided by the excessive production of roots already reported. Adven¬ 
titious root production under etiolation conditions has frequently been 
noted (Sachs (22), Godlewski(6)), and its relation to the presence of the 
functional endodermis can hardly be regarded as other than that of 
effect to cause. 
Whilst the standpoint of this discussion assumes that the elon¬ 
gating etiolated plant does not necessarily grow more actively than the 
plant in the light, but rather redistributes its growth activity in 
another way, Coupin( 3 ) has recently advanced another explanation 
of the excessive elongation in etiolation. His hypothesis, supported 
by some experimental data, assumes that in the green plant growth is 
less because retarded by some inhibiting substance formed by the 
chloroplasts in light. Coupin claims that, by adding to the nutrient 
medium of etiolated seedlings an extract from green leaves of the 
same species grown in light, he is able to control the growth of etio¬ 
lated shoots and keep them of normal length. We have attempted 
to repeat Coupin’s work as accurately as his very general description 
of his experiments has permitted, but our results have been entirely 
negative. In our experiments with Pisum sativum, 70 gms. of green 
pea shoots and leaves were chopped up and ground in a mortar. To 
this was added 30 c.c. of tap water and the mixture autoclaved for 
20 minutes. It was then put through a press and the thick syrupy 
liquid extracted was diluted 1:9 with tap water and again autoclaved. 
Eight small flat glass jars were then fitted with covers of sheet cork 
perforated to allow the radicles of the germinating peas to pass 
through. Two of these jars were filled with the diluted extract of 
green peas, two with Shive’s optimal solution ( 23 ), two with Shive’s 
supra-optimal solution, and two with tap water. The shoots in all 
cases were very nearly of a uniform length. The roots, however, 
showed considerable difference in growth. Those grown in tap water 
