46 ORGANOGRAPHY. 



We have now described all the different forms of cells, and 

 the modifications they undergo, and the combinations of them 

 which take place, so as to form vessels. The different kinds of 

 vessels and woody tissues or fibres are more or less combined 

 together, and have always a tendency to develop and arrange 

 themselves in longitudinal or vertical bundles in the parts of the 

 plant where they are found, and thus they maybe readily distin- 

 guished from the ordinary parenchyma in which they are placed, 

 both in their forms and mode of elongation. We thus find it 

 very convenient to speak of the bundles formed by the combina- 

 tion of the woody tissues or fibres and vessels, under the col- 

 lective name of Fihro-vascular Tissues, or the Fibro-vasctdar, or 

 Vertical, or Longitudinal System, to distinguish them from the 

 ordinary cellular tissue, which constitutes the Pareiichymatous, 

 or common Cellular, or Horizontal System. 



4. Epidermal Tissue. — In the higher Flowerless, and gene- 

 rally in Flowering Plants, the cells situated on the surface of the 

 different organs vary in shape and in the nature of their con- 

 tents from those placed beneath them, and form a firm layer 

 which may commonly be readily separated as a distinct mem- 

 brane. To this layer the term Epidermal Tissue is given. It 

 is generally described as consisting of two parts ; namely, of 

 an inner portion called the Ejnderynis, and of an outer thin pellicle 

 to which the name Cuticle is given. By Carpenter, however, and 

 some other authors, these terms are used in precisely the reverse 

 sense ; thus Cuticle to indicate the Epidermis, and vice versa. 

 We use the term as first mentioned, because more in accordance 

 with general usage, although it must be admitted that the name 

 Epidermis, signifying, as it does, a membrane lying upon the 

 dermis or skin, would be more appropriate if applied in the latter 

 sense. 



a. Epidermis. — This consists of one {fig. 95, a) or more {figs. 

 96, a and 97) layers of cells, firmly united together by their sides, 

 and forming a continuous membrane, except at the points where 

 it is peribrated by the Stomata, presently to be described {fig. 1 07, s). 

 These cells are generally of a flattened tabular character {figs. 

 95-99), the sides of which vary much in their outline; thus in 

 the epidermis of the Iris, and many other Monocotyledons, they 

 are elongated hexagons {fig. 92, e); in that of the Maize they are 

 zigzag {fig. 93, 5) ; whilst in the Madder, the common Polypody, 

 &c., they are very irregular or sinuous {fig. 94); and in the epi- 

 dermis of other plants we find them square, rhomboid, &c. 



Ordinarily in European plants and others of cold and temperate 

 climates, the epidermis is formed of but one row of cells {figs. 

 95, a and 99), but in tropical plants we frequently find two (fig. 

 96), three, or more, as in the Oleander {fig. 97), by which pro- 

 vision such plants are admirably adapted, as will be afterwards 

 explained, for growth in hot dry climates. The upper walls of 



