20 



STRUCTURE OF PLAINTS, CONSIDERED 



they intend at once to compliment their patrons, and to describe something 

 of the nature of the flower: thus the letters W.,Y.,0.,R.,C.,P.,V.,B.,&c., 

 when capitals, are understood to mean white, yellow, orange, red, crimson, 

 purple, violet, blue ; and hence, when a flower is named William the Con- 

 querer, or Wonder of Constantinople, its colours are understood to be white 

 and crimson ; Charming Phyllis, crimson and purple ; British Rover, blue 

 and red, Sec. It is always desirable to know the meaning of a name, or 

 even to know that it has no meaning ; in the former case some positive ideas 

 are obtained, and in both the memory is assisted. 



Sect. IV. — Structure of Plants, with a view to Horticulture. 



79. The anatomy of a plant furnishes us with numerous component 

 parts, of which we can do little else than enumerate those more imme- 

 diately connected with the practice of horticulture. 



80. Elementary organs consist of cellular tissue, or transparent vesicles 

 which adhere together so as to form a substance more or less compact, 

 which, in the leaves, fills up the interstices between the veins, and forms 

 the parenchyma. Woody fibre is an elementary organ consistmg of 

 elongated tubes, wliich are found more or less in most plants, and especially 

 in the wood and inner bai'k, among parenchymous matter. Spiral vessels, 

 consisting of elastic tissue twisted spirally within a membrane, are found 

 in the medullary sheath, but rarely in the wood, bark, and root, and they 

 scarcely exist in acrogens. Plants furnished with them are called Vascu 

 lares ; a term which includes both exogens and endogens ; and plants without 

 them are called Cellulares, in which the acrogens are included. Other forms 

 of elementary tissue are : the ducts, which are transparent tubes marked 

 with lines or dots ; the cuticle, which is a thin skin covering the leaf ; and 

 the stomata, which are pores scattered over the cuticle, or epidermis, of the 

 leaves. Grafting and budding are founded on the affinity of the elementary 

 organs in different species. 



81. Compound organs are combinations of the elementary organs, and 

 consist of the axis and its appendages ; two words which comprise the whole 

 vegetable structure. The axis may be compared to the vertebral column of 

 animals, and is formed by the development of a seed, a bulb, or other germ, 

 or of a leaf-bud. An embryo is the origin of a plant contained within a 

 seed, and it diff'ers from a bulb or bud in bemg produced by the agency of 

 sexes. When a seed or a bud is excited by its inherent vital action, the 

 tissue of which it is composed, and which has the power of generating new 

 tissue Oy the growth of one elementary vesicle out of another, developes 

 itself in three directions, upwards, downwards, and horizontally. The part 

 which descends is called the descending axis or root ; the opposite part the 

 ascending axis or stem ; and the horizontal elongations, which are chiefly 

 leaves and buds, are called the appendages of the stem. 



82. The root begins to be formed before the stem ; from which it diff'ei'S 

 anatomically, in the absence of spiral vessels, of pith, of buds, with certain 

 exceptions, and of stomata. The uses of roots are to fix plants in the soil, 

 and to absorb nutriment from it by their spongioles. 



83. The stem is generated by the development of the plumule of the seed, 

 and increased by the development of leaf-buds. If a ring of bark be cut oflF 

 from the stem of an exogenous plant, below a branch or even at the base of 

 a growing shoot of the current year covered with leaves, or if a ligature be 



