238 MANUAL OF AGEICULTURE. 



and vessels are formed by the modification of simple cells. The 

 former appear to be formed of elongated cells, which have been 

 filled up with woody substances. These firmly cohering, form 

 woody fibre. The cells of vessels are not thickened or filled up. 

 They are formed by strings of cells, so to speak, having their 

 contiguous partitions destroyed, so as to form a continuous tube 

 or channel. They possess the distinctive markings of the cells, 

 whence they are derivative. Their office would appear to be 

 that of promoting not sap but air circulation in plants. Cells 

 constitute the entire formation of some plants, such as fungi, 

 mosses, and sea plants; and these are termed cellular. They 

 have no flowers, and propagate by means of cellular germs. The 

 remaining plants are called vascular, as they contain vessels, 

 fibres, and cells. Excepting the fern tribes, they have flowers 

 more or less conspicuous, and they are reproduced by the instru- 

 mentaliiy of true seeds. 



A cellular skin or covering, called the epidejnnis, extends over 

 every part of the plant. It is divided into the cuticle or outer 

 portion, and the derma or inner portion. The cells composing it 

 are colourless, but through them shines the chlorophyll contained 

 in the cells underneath. When examined by aid of the micro- 

 scope, on its surface are seen oval-shaped organs with small 

 openings in their centres leading through the epidermis into air 

 chambers. These openings are called stomcita, and serve for the 

 purposes of perspiration and exhalation of liquids and gases. 

 They are found on all parts of the plant above ground, excepting 

 the petals or coloured portions of the flower, and they seem to 

 possess the power of opening and closing according to the moist 

 or dry condition of the atmosphere. The epidermal cells get 

 modified to assume the form of hairs and scales, as seen on leaves 

 and other parts of certain plants. 



Selecting the root as the first organ for consideration, the 

 student must make its acquaintance as the " descending axis " of 

 botanists. It is the seed's primary development, and always has 

 a downward direction. This delicate process branches into 

 numerous fibrils, whose number and dimensions rapidly increase. 

 "Eadicle hairs" are scattered over them, and through these and 

 the cells of the more delicate parts of the fibrils' epidermis is 

 absorbed the plant's nourishment from the soil. The elongation 

 of roots proceeding from their extremities, they are fitted to 

 penetrate in every direction in quest of suitable food. This 

 organ's development assumes a great diversity of form. Of 

 species, we have terrestrial roots, such as have been already- 

 described, — though it may be remarked that the roots of fungi, 

 as in the case of sea- weeds, merely serve for anchors, the fungus 

 obtaining its food from^ the atmosphere ; acj^uatic roots, belonging 

 to floating plants, which are unattached, floating freely in the 



