Ewart.- — ■ The Effects of Tropical Insolation . 477 
in alpine plants without a marked xerophilous 1 habit, might 
be distinctly injurious, owing to the difficulty of absorbing 
water from the cold ground in sufficient amount to cope 
with the rapid evaporation caused by the low pressure 
and dryness of the air. Besides, the insolation-temperature 
in alpine regions is already sufficiently high : it is at night 
and when shaded that an absorption of heat might be of 
considerable use. 
In Haematococcus and similar forms the light-protecting 
function of the red dye is probably the most important one ; 
for, as Schroder 2 and Klebs 3 have shown, the common 
presence of a red dye in the resting- spores of many Algae 
is of importance as a protection against the decomposition 
to which the chlorophyll in such cases is especially liable 
when exposed to light. Thus the green zygotes of Hydro - 
dictyon may remain living if dried in darkness, but if exposed 
to light become decolorized and die. 
Stahl considers the fact that the red colouration, which the 
young shoots of plants growing in cold climates generally 
show in spring, commonly disappears on the advent of the 
first few warm days, as being conclusive evidence pointing 
to the red dye being of importance as a means of raising 
the temperature of the young growing parts. It is however 
just when the temperature is low that the chlorophyll-grain 
is most liable to the decomposition induced by the action 
of light 4 , and when the light, if sufficiently intense, most 
markedly retards the development and turning green of the 
etiolated chloroplastid. 
If plants of Elodea canadensis 5 or Utricidaria vulgaris are 
immersed in weak sugar-solution kept at ordinary room- 
temperature and exposed to strong light, they may show 
a marked tendency to form a red dye, whereas in water or 
1 Lazniewski, Beitrage zur Biologie der Alpenpflanzen : Flora LXXXII, 1 896, 
pp. 224-267. 
2 Schroder, Bot. Untersuch. Tiibingen, Bd. ii, Hft. 1, 1886. 
3 Klebs, Bot. Untersuch. Tiibingen, 1883, Bd. i, Hft. 2. 
* See Assim. Inhibition: Journal Linnean Society, 1896, p. 390 (Coniferse). 
5 Assim. Inhib. : Journal Linnean Society, Vol. xxxi, 1897 (Botany), p. 567. 
K k % 
