CHAMBERS'S INFORMATION FOR THE PEOPLE. 



anything like details. It is even difficult to attempt 

 any classification of them ; for, though differing in 

 their properties and external appearance, many of 

 them are identical in chemical composition, and, 

 subjected to peculiar treatment, readily pass into 

 new and singular combinations. Some, for instance, 

 are saccharine, as the juice of the sugar-cane. 

 Many are oleaginous, balsamic, or resinous ; some 

 are narcotic, aromatic, or mucilaginous ; while 

 others are astringent, purgative, or poisonous. For 

 examples of these divisions, we have such sub- 

 stances as palm and olive oil, myrrh, resin, opium, 

 camphor, gum-arabic, tannin, gamboge, prussic 

 acid, aloes, colocynth, and many others of every- 

 day familiarity. 



Besides the proper excretions and secretions, 

 there are several adventitious substances found in 

 plants, which are not the products of vital organi- 

 sation. Lime, for instance, is found in the ashes 

 of many plants in union with acids ; sometimes it 

 is excreted in the form of a thin crust on their 

 leaves, and in other cases in peculiar cells. Silica 

 also occurs in considerable quantities, especially 

 in the stems of reeds and grasses; it forms the 

 glossy pellicle of the cane, and is sometimes found 

 in the joints of the bamboo, where it is deposited 

 in a soft pasty mass, called tabasheer, which ulti- 

 mately hardens into pure semi-transparent silica, 

 Eguisetum hyemale, called Dutch -rushes, con- 

 tains a large quantity of silica, and is used for 

 polishing mahogany. Besides these earths, there 

 are various metallic oxides and salts, and the well- 

 known alkalies potash and soda. The physio- 

 logical uses of such products are but imperfectly 

 known. Many of them such as starch, gum, 

 sugar, and the fixed oils directly administer to 

 the support of the young plant and to the forma- 

 tion of new tissues. Others, again such as silica 

 and metallic oxides give hardness and stability 

 to the stems and branches; some give elasticity 

 and pliancy to the young shoots, thereby prevent- 

 ing them from being broken by winds ; and several 

 as tannin, for example seem to administer to 

 the durability of the woody tissue. 



METAMORPHOSES OF PLANTS. 



The metamorphoses of plants, in the general 

 sense of the term, form one of the most interesting 

 sections of Vegetable Physiology. Technically, it 

 is termed Morphology that is, a consideration of 

 the changes and transformations which various 

 parts of plants undergo, either from natural or 

 artificial causes. We know, for instance, that 

 many plants are made to change their appearance 

 and qualities by cultivation ; that by grafting, hy- 

 bridising, and other means, the gardener can 

 change the size, colour, and qualities of his fruits 

 and flowers : and that analogous changes take 

 place in a state of nature such as the conversion 

 of petals into leaves, and leaves and branches into 

 thorns and spines. It is also well known that 

 flowers become double by changing their stamens 

 into petals ; and it is from a knowledge of such 

 facts that botanists have asserted that all the parts 

 of the flower and fruit, as well as the appendages 

 80 



of the stem or ascending axis, are modifications of 

 a single typical organ, and may be considered as- 

 leaves adapted to special purposes. 



The law which it seeks to establish may be stated 

 to be this : that all the appendages of a plant have 

 a common origin with the leaf, and may therefore 

 successively assume the form and appearance of 

 that primary organ. The branches of the stem, 

 take their origin from leaf-buds, and are clothed 

 with branches and leaves by the same process as- 

 5n the main stem. Towards the point of fructifi- 

 cation, the leaves assume the form of bracts ; these, 

 again, are succeeded by the leaf-like sepals of 

 the calyx; and next by the petals of the corolla. 

 Within the petals are the stamens which some- 

 times assume a leafy form next the pistil, and 

 ultimately the seed-vessels. Even the seeds are 

 but leaves in another form. Thus, the growth and 

 reproduction of plants may be regarded as a circle 

 of leaf-like changes, the leaf, or some modification, 

 of it, being in all cases the organ which administers 

 to the functions of vitality. As there is an indubi- 

 table passage from leaves to every other organ, so 

 may any one organ be found to revert to the 

 primary form of the leaf. In the double-flowering; 

 cherry, so common in shrubberies, the stamens are 

 changed into petals, and the ovary into a green 

 leaf! 



The hybridism of plants is closely allied to the 

 subject of morphology, and is, in fact, a process of 

 transformation of an artificial character. As among 

 animals two distinct species of the same genus will 

 produce an intermediate offspring such as the 

 mule, which is the offspring of the horse and ass 

 so among vegetables, two species belonging to the 

 same genus can be made to produce a hybrid; 

 that is, a new plant possessed of characters inter- 

 mediate between its parents. This power of hy- 

 bridising is more prevalent among vegetables than 

 animals ; for the different species of many genera 

 of plants are capable of producing this effect, if the 

 pollen of one species be put upon the stigma of 

 another. And this crossing may even be applied 

 to separate genera. Hybrids have not the power 

 of perpetuating their kind like naturally distinct 

 species ; for, though occasionally fertile in the 

 second and third generations, they have never 

 been known to continue so permanently. But 

 though incapable of propagating beyond a limited 

 period, the pollen of the parent species may be 

 made to fertilise them, or their pollen to fertilise 

 the parent; but in either case the new offspring 

 gradually merges into the original species. Thus 

 nature has wisely set a limit to the intermingling 

 of species, by which they are preserved from 

 ultimately running into confusion and disorder. 

 In an economical point of view, hybridism is of 

 great value to man. By a knowledge of its prin- 

 ciples, he has been enabled to modify the characters 

 of natural species, so as to adapt them to his spe- 

 cial purposes ; and thus have arisen most of those 

 beautiful varieties of what are termed florists' 

 flowers, which now adorn the flower-garden. So 

 also by crossing varieties of the same species, our 

 grains, fruits, and kitchen vegetables have been, 

 brought to a high state of perfection. 



