Vegetable Physiology, 85 



vessels, receptacles of the juice, reservoirs of the proper or pecu- 

 liar fluids, or accidental reservoirs. Although destitute of lining 

 membrane, their walls are generally compact, being formed of 

 condensed cellules. They vary in size and form, and though of- 

 ten quite regular, sometimes have no definite figure or arrange- 

 ment. This is the view taken of these proper vessels by some 

 botanists, while others consider them to be not simply cavities 

 between adjacent cells, but a separate form of tissue, to which 

 they give the name of branching vessels. They are found on the 

 lower sides of leaves, and in the bark, and the sap or proper 

 juice is carried by them from the leaves, where it is produced, 

 down the bark, and thence to other parts of the structure. 



Of these modifications of membrane and fibre, are formed all 

 the parts of plants. The varied combinations of the vascu- 

 lar and cellular tissues give rise to an endless variety of struc- 

 ture and external form, and produce an equal diversity in the 

 properties of the juices and secretions. Many plants, as we 

 have seen, are entirely composed of cellules, but the greater 

 number, of both cellules and vessels. The compound organs 

 of plants, as the leaves and flowers, which are formed of com- 

 binations of these, will be described hereafter. There are, 

 however, parts more or less complex which may also be con- 

 sidered as elementary. These are the cuticle, epidermis, or gen- 

 eral envelope of plants, and the organs immediately connected 

 with it. This is a modification of cellular tissue in the form of 

 a delicate membrane. In young plants it extends over the 

 whole external surface, from the fibrils of the roots to the 

 leaves, the petals of the flower, and the fruit. From the leaves 

 of some plants, as the Iris, it may be easily stripped, without 

 any preparation, and from others, after being soaked in water. 

 It is usually transparent and colorless, and is found to consist 

 of flattened cells containing air. The form of these is various 

 in different plants, some being regularly oblong, and some, as 

 it were, dove-tailed into each other. Sometimes these layers 

 of cells are single, sometimes arranged in two or three series. 

 Over all these is an extremely delicate film, perforated by 

 minute oblong pores. The use of the cuticle appears to be to pre- 

 vent the moisture of the soft tissues beneath it from evaporating. 

 Accordingly, it is absent in all plants which live beneath thesur- 



