A manual of physiology : including physiological anatomy / by William B. Carpenter.

  • William Benjamin Carpenter
Date:
1856
Catalogue details

Licence: Public Domain Mark

Credit: A manual of physiology : including physiological anatomy / by William B. Carpenter. Source: Wellcome Collection.

    125/690 (page 93)
    find the most succulent plants,—such as the Sed ums or * stone- crops' of our own country, and the Cacti and Euphorhice of the 'tropics,—in dry exposed situations, where they seem as if they would be utterly destitute of nutriment. The fact is, however, that they lose their fluid by exhalation very slowly, in consequence [of their small number of stomata; whilst, on the other hand, they absorb with great readiness during rainy weather, and are enabled, iby the fleshiness of their substance, to store-up a large quantity of imoisture until it may be required. In some parts of Mexico, the Iheat is so intense, and the soil and atmosphere so dry, during a [large part of the year, that no vegetation is found at certain seasons, save a species of Cactus; this affords a wholesome and refreshing article of food, on which travellers have been able to subsist for [many days together, and without which these tracts would form iimpassable barriers. On the other hand, the plants of damp situa- ftions usually exhale moisture almost as fast as they imbibe it ; and [consequently, if their usual supply be cut-off or diminished, they [soon wither and die. Plants that usually live entirely submerged, [are destitute of the cuticle or thin skin, which covers the surface in [other cases; in consequence of this, they very rapidly lose their jfluid, when they are removed from the water; and they are hence 'dependent upon constant immersion in it for the continuance of Itheir lives, although their tissues may not be remarkable for the (amount of fluid which they contain. I 154. There are some Plants which are capable of adapting them- selves to a great variety of situations, differing widely as to the [amount of moisture which their inhabitants can derive from the soil land atmosphere; and we may generally notice a marked diffei-ence in the mode of growth, when we compare individuals that have grown under opposite circumstances. Thus a plant from a dry exposed situation shall be stunted and hairy, whilst another, of the same species, but developed in a damp sheltered situation, shall |be rank and 'glabrous' (smooth). But in general there is a certain iquantity of moisture congenial to each species; and the excess or deficiency of this condition has, in consequence, as great an influence in determining the geographical distribution of Plants, as the amount bf light and heat. Thus, as already remarked, the Orchideee and Tree Ferns of the Tropics grow best in an atmosphere loaded with 'dampness; whilst the Cactus tribe, for the most part, flourishes [best in dry situations. The former become stunted and inactive, |if limited in their supply of aerial moisture; whilst the latter, if too copiously nourished, become dropsical and liable to rot. Among •the plants of our own country we find a similar limitation ; a moist [boggy situation being indispensable to the growth of some, whilst [a dry exposed elevation is equally essential to the healthy develop- ment of others. There is a beautiful species of exotic Fern, the ^Trichomanes speclosum, the rearing of which has been frequently