60 THE CUTICLE OF HERBS. 



necessary that they should possess the rudeness and strength of texture which appro- 

 priately belong to plants that have to combat the power of the elements through a 

 long series of years. 



The stem, for the most part, is small, seldom attaining to a greater diameter than 

 one and a-half inch ; and, with the exception of twining plants, and such grasses as 

 the bamboo, do not exceed six feet in height.- The structure is delicate, being composed 

 of cellular tissue of a somewhat loose kind, with bundles of woody fibre running at 

 intervals from the root upwards. They are thus but ill-fitted to resist the influence of 

 strong winds, or the destructive propensities of animals. There are, however, some 

 circumstances which tend to increase their strength. Such are firsty the cylindrical 

 form of the stem ; secondly, the hollowness of the stem ; and, thirdly, the inclosure of the 

 stem by a tough cuticle or bark, and, in sqrne instances, a further layer of silica or flint. 

 That the cylindrical form is stronger than any other is well known ; but it may not be 

 so commonly understood that a hollow cylinder, with moderately thick walls, is 

 stronger than a solid rod of the same material. Thus that vacuity, which at first sight 

 is indicative of weakness, is really fitted to impart increased strength. The cause of 

 the hollowness is the more rapid development of the perpendicular than the horizontal 

 layers of the stein. 



The stem of an herbaceous plant thus consists of three parts : a central pith, which 

 is frequently wanting ; an external envelope or skin ; and an internal mass of cellular 

 tissue and woody fibre. The pith is composed of cellular tissue, of the hexagonal or 

 octagonal form. The woody fibre of the stem is not found in even layers, but in bun- 

 dles lying detached from each other, as may be readily seen by tearing a stem across, 

 when the bundles of tough fibres will be stretched, and project somewhat from the 

 broken surface. It may also be seen through the cuticle of the common parsley, in 

 ribs passing in parallel lines from the root upwards into the leaves. Each bundle is 

 usually inclosed in a mass of cellular tissue, to which it gives firmness. 



Cuticle. The cuticle of herbs is an interesting structure, and the seat of a large 

 part of the respiration and digestion which proceeds in those plants. It consists of two 

 layers an epidermis or scarf-skin, and a true skin, with certain appendages viz., 

 stomata, hairs, prickles, warts, and reservoirs of secretions. 



The Epidermis is a layer of inspissated organic mucus, which sometimes may be 

 readily detached from the cuticle, 

 as in the common box-leaf, but 

 at others requires maceration in 

 water for some time before its exist- 

 ence can be demonstrated. It 

 covers all the external surface of 

 the plant, except the stomata and 

 the free end of the stigma, and it 

 even forms a covering for the hairs. 

 Mohl considers it to be a secretion 

 poured out from the external sur- , 6> outer layer of the cuticle, composed of compressed cells, 

 face of the cells, the walls of the d > a subjacent layer of larger cells, with vacuities, or pareii- 

 cells themselves being at the same c , S?S5&g%^S& the cutide to the air 

 time thickened by internal depo- cavities above. 



Bits. It is not a cellular structure, although, when removed from the surface of the 

 cuticle, it has a cellular outline ; but is a simple layer, with markings corresponding to 



