228 
POrULAU SCIENCE EEVIEW. 
green colour of healthy vegetation, which is due to the pre- 
sence in the cells of a substance called chlorophyll. There can 
be little or no doubt that this is the main agent in the assimi- 
lation of carbon. It is well known that plants deprived of 
sunlight develope none of this green colouring matter, and that 
their tissues are weak and flabby ; 
Pale, fleshy, as if the decaying dead 
With a spirit of life had been animated. 
Such plants cannot take up carbon-dioxide; on the contrary, 
and this is also true of the parts of all plants which are not green 
— as the bark and the flower — they expire that gas, and so vitiate 
the atmosphere like animals. 
By these processes the plant increases in size and complexity, 
and at the same time is able to store up in its tissues starch 
and other carbonaceous substances to be employed as fuel during 
the flowering and fruiting seasons. These reproductive functions 
do not commence till a period pretty definite in the life of the 
species, when, instead of unfolding green leaves, the buds pro- 
duce those variously modified organs which form the flower and 
the end of all of which is directed to the production of ripe 
seed. The process of their evolution, and the changes they pass 
through, are all wasteful to the plant and involve the consump- 
tion of its hoarded stores : so great an effort is flowering that it 
frequently causes the death of the plant. 
The modifications in external anatomy which are met with in 
parasites are chiefly in the organs of nutrition. Disregarding 
altogether for the present the green parasites, such as the 
Mistletoe and Loranthus, the first thing that strikes the ob- 
server is the absence of leaves. True there are not wanting a 
few fleshy or dry scales, but of green foliage, and indeed of 
green colour at all, the plants are absolutely devoid. Nor can we 
find root-hairs ; indeed, in many no root at all can be said to 
exist, but where there is a branched root, it possesses instead of 
root-hairs suckers applied to the tissues of the supporting plant. 
Even the supporting axis may be greatly reduced, and so the 
whole nutritive system be wanting, as in the Rafflesiaceoe^ 
where the base of the flower is in close apposition to the tissues 
of the alien stem upon which it grows. From this extreme case 
we may pass to parasites with a short axis closely covered with 
large scales (Cytinus), with a prostrate, half-buried rhizome, 
angular and branched (Hydnora) or very large and swollen 
{BalanophoTaceoe), and so reach plants with an erect, well- 
developed scale-bearing axis, as the Broomrapes {Orohanche). 
In another type, as Dodder {Cuscuta) and Gassytha^ the axis is 
present in the form of long slender twining threads, upon which 
are placed the absorbent suckers, but scarcely a vestige of any 
