108 
POPULAR SCIENCE REVIEW. 
in darkness. Up to a certain point this takes place gradually, but beyond 
this, it increases to a considerable extent, and the internal surface of the 
pericarp exhibits certain alterations of structure. The greater the tempera- 
ture, the larger will be the volume of carbonic acid exhaled. Nearly the same 
amount of carbonic acid is evolved during the two periods of approaching 
maturation and approaching decay. But once the latter stage has been arrived 
at, the quantity of exhaled carbonic acid increases rapidly. The proportions 
of gases contained in the juices were thus estmiated : — The juice, having been 
expressed, was placed in vessels, and the gases expelled by ebullition. It 
Avas found in this way that carbonic acid and nitrogen are present in various 
proportions, but that none of the following exist in fruit juice : — Oxygen, 
hydrogen, carbonic-oxide, carburetted hydrogen. When ripe fruit is enclosed 
in an atmosphere of am it absorbs hydrogen Avith great rapidity, and if it is 
alloAved to remain till it has become soft, it is found to contain a large propor- 
tion of gas rich in carbonic acid. 
Connection hetioeen the Geogra^ohical Distribution and External Characters 
of Plants. — Some time ago Dr. Wehvitsch, the celebrated African botanist, 
presented a memoir upon a remarkable species of Cissus, from the south 
of Benguella, in which, whilst describing forty distinct species of the family 
Ampelid£e, he shoAved that these plants were interesting to the plant 
geographer, as well as to the botanist. The forty species described by Dr. 
Welwitsch are spread over a space of 300 miles from east to Avest, com- 
mencing with the burning sandy steppes of the Atlantic coast region, and 
extending into the richly-Avooded, cool, elevated plains of the interior. 
Throughout this space the number of species increases gradually, and the 
number of individuals becomes continually greater. It is found that 
the species Avdth thick, sappy, fleshy stems preponderate in the littoral 
region, that is, within a height of 1,000 feet from the leA^el of the sea ; 
those Avith elongated tAvining stems, in the regions of the primeval 
forests ; and the species with upright scarcely twining stems, in the 
highest regions of the elevated plains of the ulterior. Another charac- 
teristic accompanying the geographical distribution of the Angola species of 
Cissus is the hairy covering of the stem and leaves. The species of the 
littoral region, for the most part, exhibit bright green, and but slightly green 
stems and leaves, whilst the species of the primeval forest region are 
characterised by dark green shining foliage, and more or less leathery, some- 
times even evergreen leaves. On the other htind, m almost all the species of 
the region of the elevated plains, a thick, hairy, or even felt-like covering 
is seen on the stem and leaves. In a species Avhich occurs on the gneiss rocks 
of Pungo-Andongo, this latter covering forms such a thick golden-brown pile 
that the entire plant has the appearance of having been hewn out of pine 
copper, and is indisputably one of the most beautiful of the vegetable pro- 
ductions of Angola. This species Dr. Welwitsch has termed Cissus Living- 
stoniana, in honour of our distinguished felloAv-countryman, Dr. Livingstone. 
— Vide Proceedings of the Linncean Society, vol. viii., 1864. 
CHEMISTEY. 
Action of Light onSantonine. — Most of our readers are aware that santonine, 
which is a peculiar principle derived from plants of the composite order. 
