20 



HISTORY OF THE VEGETABLE KINGDOM. 



and are destitute of buds; as the heaths. Trees, 

 )iaving trunk branches, buds. 



Solid, when the stem has no internal cavity; as 

 most trees, the sugar cane. 



Fistulous, or hollow, with an internal canal, 

 either continuous or divided by partition, at 

 intervals; as in grains, grasses, bamboo cane, &c. 



Pitky, or medullary, fitted with a large pith; 

 as in the elder. 



Soft, when it is unable to support the erect 

 position, and falls to the ground. Firm, flexible, 

 brittle, svemhnt, are other terms which suffi- 

 ciently explain themselves. 



In shape, the stem may be cylindrical, com- 

 pressed, angled, knotty, jointed, geniculated, or 

 bent at the joints in the form of the knee, 

 climbing, when it coils round other stems. 



Sarmentaceo^is, when it ascends trees, or other 

 bodies, by means of tendrils or other peculiar 

 appendages. 



Simple, without ramifications, as in the fox- 

 glove, white mullein. 



Branched, divided into branches and twigs. 



Dichotomous, dividing into two forked branches 

 on bifurcations. Trichotomws, into three. 



Vertical, stem growing erect. 



Prostrate, or procumbent, when it lies on the 

 ground. 



Creeping, when it trails on the ground, taking 

 root at certain joints. 



Tortuous, forming curves in different directions. 



Spiral, curving in a regular screw form. 



Leaf-bearing, having leaves ; leafless, the re- 

 verse. 



Scaly, having leaves placed in the fonn of scales. 



The stem may be either smooth or dotted, 

 hairy, glaucous or powdery, spinous or thorny, 

 prickly. 



Internal form of stems. The structure of stem s 

 proceeding from a two lobed (or dicotyledonous) 

 seed, differs considerably from those growing 

 from a one lobed or monocotyledonous seed; 

 hence, the two first great divisions of the vege- 

 table kingdom already alluded to. We shall 

 proceed first to describe the dicotyledonous stems. 



When we examine a piece of the trunk of a 

 tree, such as the oak or elm, we find it com- 

 posed of tlie following parts. 



In the centre is the pith or medulla, a; then 

 the solid woody mass of 

 the trunk, in successive 

 circles, from the central 

 pith outwards. The 

 outer woody circle of 

 newest formed wood or 

 aOmrnvm, b. Immedi- 

 ately investing this, the 

 liber or inner bark, c; 

 between the inner bark, 

 c, and the epidermis or 

 outer skin, d, is a soft 



green juicy matter, called the herbacemis en- 

 velope and cortical layers, e. 



The epidermis, cuticle, or outer skin, is a part 

 common to all organized beings both of the 

 vegetable and animal kingdom. In vegetables 

 it is a thin, nearly transparent layer, formed of 

 a uniform tissue, which appears composed of 

 cellules varying extremely in form, and present- 

 ing numerous small openings or pores, which 

 some authors consider as a kind of inhaling 

 mouths. The epidermis envelopes all parts of 

 the vegetable ; but it is more especially apparent 

 on young stems, from which it may easily be 

 separated with a little caution. It possesses 

 only a certain degree of extensibility, and when 

 stretched beyond this point, by the enlargement 

 of the tnink, it tears and splits, as is observed in 

 the oak and elm, or it is detached in flakes or 

 plates, as in the birch and plane. When re- 

 moved from a young stem, it is reproduced with- 

 out difficulty. It is the part of the vegetable 

 that resists decomposition longest, and putrefac- 

 tion has no perceptible action upon it. The 

 colour which it presents is not inherent in 

 its nature, but is derived from the peculiar 

 colouring of the tissue on which it is applied. 

 Hence the green colour so prevalent in the 

 leaf and tender shoot, which the transparent 

 epidermis merely transmits, and the beautifiil 

 variety of lines displayed in flowers and fruits. 

 And yet the colour is sometimes inherent, even 

 in the epidermis itself, as may be seen by inspect- 

 ing that of the lower part of the petals of the 

 crocus. In the permanent parts of woody and per- 

 ennial plants, the old epidermis often disengages 

 itself spontaneously, as in the currant, birch, and 

 plane tree ; in which it seems to be undergoing 

 a continued waste and repair, and in such parts 

 it is again regenerated, even though destroyed 

 by accident. But in herbaceous plants, and in 

 tlie leaf, flower, and fruit of other plants, it never 

 disengages itself spontaneously, and is never 

 again regenerated, if once destroyed. 



The nature and origin of the epidermis fonn 

 two rather obscure subjects in vegetable anatomy. 

 Some authors say, with Malpighi, that the epi- 

 dennis is not a membrane distinct from the rest 

 of the vegetable tissue. They consider it as 

 formed by the outer wall of the subjacent 

 cellules, belonging to the herbaceous tissue, 

 hardened by the continued action of the air and 

 light. Others, again, concur with Grew in con- 

 gidering it as a perfectly distinct membrane, 

 simply applied upon the subjacent cellular 

 tiasue. The microscopic observations of Pro- 

 fessor Amici throw much light on this question, 

 and seem to confirm the second of these opinions 

 According to that naturalist, the epidermis is a 

 membrane entirely distinct from the cellular 

 tissue upon which it is applied. And in this 

 respect, it closely resembles the out«r skin of 



