390 Eu'art . — The Action of Cold and of 
phyll proceed simultaneously in every chloroplastid exposed 
to light, and that the former process is more rapid than 
the latter when the light is strong, then the apparently 
more rapid bleaching at the end of the exposure might 
be due to the reformation of chlorophyll having ceased to 
take place, and this would indicate that fresh chlorophyll 
can normally be produced with great rapidity, though not 
much more rapidly than the chloroplastids of Spirogyra 
[ ca n form starch 1 . It is, however, extremely difficult to 
estimate changes of coloration by comparison with the 
surrounding chloroplastids so long as the exposed ones 
are distinctly green, and the same loss of chlorophyll which 
converts a pale green chloroplastid into a colourless one 
may cause no perceptible difference in the coloration of 
a dark green one. As a matter of fact, the leaves of many 
plants may yield a much weaker extract of chlorophyll after 
a day’s exposure to strong light than is obtained from 
a similar bulk of shaded leaves, although the eye may be 
unable to detect any difference in the depth of coloration 
of the two sets of leaves, and hence it is doubtful whether 
the apparently more rapid decomposition of chlorophyll as 
the chloroplastids become fatally affected is not simply an 
optical delusion. 
Assuming that this peculiarity does actually exist and 
cannot be entirely explained by the facts already given, 
it might be possible that the chlorophyll, when in organic 
connexion with a living plastid, is more resistant to the 
oxidatory photo-chemical action of sunlight than it is when 
isolated, or when the organic union is disturbed or de- 
stroyed. If plants of Elodea are killed by chloroform, and 
exposed in well-aerated water to the action of bright light 
for a day, including nearly three hours’ intermittent sunlight, 
all the exposed leaves are completely bleached, whereas 
a normal healthy plant subjected to the same exposure 
retains a healthy green colour, though perhaps slightly paler. 
1 G. Kraus, Jahrb. f. Wiss. Bot., 1869-70, Bd. vii, p. 511. 
