September 20, 1883. ] 
JOURNAL OF HORTICULTURE AND COTTAGE GARDENER. 
253 
which contrasts very markedly with the rich-coloured portion. These 
tints, however, vary considerably in depth, brightness, and clearness, 
and the value of the plant varies proportionally to its merits in these 
respects. The flowers are usually borne singly from the top of the small 
bulbs, but occasionally two may be produced, though this is compara¬ 
tively rare. In many collections it is now flowering freely, and a quality 
of inestimable value at this time of year when Orchid flowers are so 
scarce is the great time they last in beauty. Under favourable condi¬ 
tions flowers will remain upon the plants for six weeks, continuing 
attractive from September till the beginning of November. 
GARDEN CHEMISTRY. 
HYDRO-AERIAL ELEMENTS. 
Plants, like animals, find a large portion of their sustenance in 
air and water. "Water pure and simple—that is to say, uncombined, 
contains about half its weight of water. Then the dry matter of 
organic beings is largely made up of the elements of water. Water 
is composed of hydrogen and oxygen (IDO) ; and starch, sugar, gum, 
fat, wood are all composed of these elements, to which carbon has 
been added. Gluten, fibrin of Wheat and of flesh, and other so-called 
nitrogenous matters are also composed of these with a further addi¬ 
tion—15 or 16 per cent.—of nitrogen with a little sulphur and phos¬ 
phorus. Even when every part of water is expelled these elements, 
hydrogen, oxygen, carbon, and nitrogen, form not less than 95 per¬ 
cent. of garden plants, and oftener over 98. The rest is the mineral 
matter which is left as ash when plants are burnt. We have seen 
that the most valuable part of this ash is phosphoric acid, potash, lime, 
magnesia, &c., and that it is not only absolutely necessary but very 
scarce in most soils and even manures. Hence their high money- 
value. 
These substances come from the soil only, and, when deficient, 
fertility fails unless these are added. Hence their paramount im- 
FiC. 48—CATTLEYA 3IARGINATA. 
forms the greater part of all vegetable substances and all flesh. An 
average man weighs about 140 lbs., and of that no less than 101 lbs. 
are pure water. Many animals are even more watery. Cucumbers 
grown on the “ express ” system have the appearance of solids, but 
in reality are very nearly all water. Many fruits contain over 90 per 
cent ; rapidly grown Water and other Melons and berries often as 
much as 95. When one thinks of this the fact of old Mehemet Ali 
consuming his 40-lb. Melon after dinner becomes understandable, 
and we can also understand that the huge Water Melons consumed in 
Spain and in the warmer regions of America are in reality not solids 
but liquids, and are evaporated accordingly. Then “ dry bread 
portance despite their small proportion in soils and in plants. They 
have been called soil-elements. The carbon, hydrogen, and oxygen 
have been called hydro-aerial elements, because these the plants find, 
in air or soil in the form of carbonic dioxide and water. At another 
place we will consider how these compounds, water and carbonic.- 
dioxide, are changed. At present we will consider the source of 
them—where they are found. That familiar substance water we may 
at once dismiss in so far as regards its being the source of the hydro¬ 
gen and oxygen in carbo-hydrates. Its composition has already been 
given. 
Something more must be said about carbonic dioxide. As its 
