464 Ewart . — The Effects of Tropical Insolation . 
which such shade-plants are especially liable when accidentally 
exposed to prolonged intense illumination. 
In trees or shrubs growing more or less in the open and 
with foliage which is red when young, it can plainly be seen 
that the young foliage formed in more shaded positions is 
less red than that which is more exposed ; whereas according 
to Stahl’s theory the reverse should be the case. The more 
exposed leaves also retain their red colour longer and to 
a later stage of development than the shaded ones, in those 
cases in which the leaves lose their red colour when adult, as 
is shown well by Ancistrocladus Vahlii. Owing to the tonic 
stimulating action which light exercises, the more exposed 
leaves are larger, broader, and develop more rapidly, than 
very much shaded ones. Hence, owing to the chlorophyllous 
tissues developing and reaching their adult and most resistant 
condition more rapidly, the red colouration may disappear 
from the more exposed leaf in an actually slightly shorter time, 
though it persists to a later stage of development and size in 
the more exposed leaf than in the markedly shaded one. 
That many plants growing in the shade form a greater 
or less amount of red pigment is quite true : but in all the 
cases observed the red colour is most marked when the plant 
is growing in more exposed situations, and in extremely shady 
habitats it may almost or entirely disappear. The inference 
simply is that such plants are extremely sensitive to and 
readily injured by exposure to light of at all marked 
intensity : whilst it has already been clearly established that 
very marked differences do actually exist in the sensitiveness 
of different plants to light in correlation with the amount of 
exposure to which they are subjected in their natural habitat. 
In the Filicineae it is possible to formulate the general rule 
that hygrophilous Ferns growing in damp and shady places 
are always green ; whilst in more or less xerophilous Ferns, 
growing in more exposed and drier habitats, a marked red 
colouration is frequently present. Thus in Blechnum orientate , 
growing in an exposed and rather dry situation in the gardens 
at Peradeniya, the young leaves have a marked red coloura- 
