M. Boussingault, who has studied vegetation in darkness, finds that the leaves of a vegetable which has never had any light at all, in its first appearance and development, never exhales oxygen, its respiration furnishes carbonic acid gas only. The plant, therefore, breathes just as an animal does. We must observe in this case that the substance of the seed only supplies this product. The plant borrows nothing from without, consumes nothing but the elements which were contained in the seeds, and dies when those nutritive elements are exhausted. The duration of its existence depends entirely on the weight of the seed whence it has sprung. If a well-developed plant be kept in darkness, the same fact may be observed. The plant gives out nothing but carbonic acid, and, as it borrows nothing from without, it perishes when it has thus devoured its own substance. M. Sachs says, in his _Physiologie Végétale_, that the movements proper to the leaves of many vegetables cannot take place if the plant is kept in darkness. Plants so kept remain always in the condition which Linnæus defined as _sleep_. Flowers contained in natural coverings, which in a great measure debar them from the light of the sun, do indeed produce colours, but those flowers are formed inside their natural coverings, at the expense of substances contained in their leaves, which could not be produced except under the influence of light. The same truth applies to fruits. Leaves, flowers, fruits, are then, as the German physiologist, Moleschott, has said, "beings woven of air by light." The same author adds: "When we contemplate the brilliant colours of the flowers, and when their delicious perfume gives serene satisfaction to that poetic faculty which exists, though it may slumber deeply, in the soul of every man it is still the light which is the mother of colour and of perfume." The influence of the sun on vegetation is of fundamental importance. Without the sun no plant would grow upon our globe. In those regions which are permanently deprived of the powerful and beneficent torch of nature, towards the extreme north, all vegetation is stunted, and higher still, it does not exist. Absence of light, and cold, are the causes of the complete disappearance of the natural adornment, and the useful tribute, which elsewhere vegetation furnishes to the earth. In the hot regions, vegetation is vigorous and extensive, in proportion to the abundance of sunshine poured upon them. There is nothing to be compared to the luxuriant vegetation of the tropical countries in both hemispheres. The vegetation of Brazil, of equatorial Africa, and the inter-tropical regions of India, is renowned for its abundance and variety.