DR. A. J. EWART ON ASSIMILATORY INHIBITION. 565 
the horizontal branching stems remain living, and from them 
short condensed colourless or pale yellow shoots arise, the cells 
of which are packed with starch grains. These, if the weather 
be favourable and warm, grow and emerge above the surface of 
the mud and then become slowly green ; but the leaves are small, 
packed with starch grains, and show only a weak power of 
assimilation, which, where the starch is especially abundant or 
the green coloration only slight, is imperceptible. When the 
winter frosts commence all the parts above ground are killed, 
only the underground part of the stem and the attached etiolated 
amyliferous winter shoots buried in mud can survive the winter 
and recommence growth next spring *. The amyliferous leaf- 
cells seem to contain no chloroplastids ; the mass of starch grains 
with which the cell is filled may either be colourless or have 
a distinctly yellowish or occasionally brownish tinge. Close 
examination shows that each starch grain or group of starch 
grains is imbedded in a matrix, which is really the body of an 
amyloplast and with it forms a thin brown film enclosing the 
blue starch grain. 
Etiolated shoots brought to a temp. of 20° C. and exposed to 
light begin to elongate distinctly in a day or two, the starch 
grains to disappear, and the chloroplastids to become distinctly 
visible. After 3 days the chloroplastids are still pale yellowish 
green, and assimilation is weak or imperceptible. After 5 days the 
starch grains are very much reduced in size, and in many chloro- 
plastids have disappeared. The latter are still not so deeply 
green as normal, assimilation in a few leaves is fairly active, in 
most is weak, and in a few still imperceptible. In all cases the 
amyloplast finally loses its starch owing to the growth of the leaf 
using up more plastic material than is supplied by the still weak 
assimilation, and becomes a normal chloroplastid. No destruction 
or disappearance of * primary amyliferous chlorophyll grains” 
followed by a new formation by plasmatic differentiation of 
* secondary normal assimilatory chlorophyll grains” takes place. 
Apparently in the etiolated condition the leaves of Elodea 
have no power of assimilation, this becoming perceptible only 
when the chlorophyll grains are distinctly greenish. The 
* Herein lies the explanation of the fact that Elodea, though all vegetative 
parts are killed by being frozen, and though it neither fruits nor forms special 
resistant propagula or bulbils, can nevertheless survive in Northern Europe, 
year after year, during even severe winters. 
