INTRODUCTION TO BOTANY. xix 
II. Anatomy anp Puystonocy. 
os 
[Abridged from the writings of Professor Lindley and Professor Asa Gray.] 
150. Vegetable Anatomy, or the study of the microscopical structure of the com- 
pound organs of plants, and Vegetable Physiology, or the study of the functions which 
each organ performs during life, are distinct and extensive branches of botany, with 
which ae merely mes tic or ps seg Sor nrg who uses a Flora for the pur- 
pose of ascertaining names 0} ts. not necessarily much concern. In 
this outline, therefore, we shall touch on these cognate sciences very briefly. ‘i 
§ 1. The elementary Organs. 
151. If a very thin slice of a plant (say, of a succulent leaf or fruit) be magnified, 
it will be found to be made up of variously and arranged ultimate parts or 
elementary organs, forming a sort of honey-combed structure. These ultimate parts 
are called cells. _ . 
152. A cell, in its simplest state, is a closed membranous sac, formed of a sub- 
stance permeable by fluids, though usually destitute of visible pores. When cells 
are combined, the mass is called a tissue ; but each cell is a distinct individual, sepa- 
rately formed and separately acting, though cohering with the cells with which it is 
in contact, and partaking of the common life and action of the tissue of which it 
forms a part. The membranes separating the cells are called their walls. 
153. Botanists usually distinguish the following tissues, 
(a) cellular-tisswe, called also pulp and parenchyma, consists of roundish, ob- 
long, cylindrical, hexagonal, or stellate thin-walled cells, and is found in 
every plant. All the soft parts of leaves, the pith of stems, the pulp of 
fruits, and all young growing parts are formed of cellular-tissue ; and 
very many cryptogamic plants possess no other tissue. In it also are 
centered the most active functions of the living vegetable. It is the 
first tissue formed, and continues to be formed while growth continues, 
G and when it ceases to be active, the pales ee a 
b) woody-tissue, or pleurenchyma, consists of long, tapering t 
: each end, of a thicker, stronger, and much tougher substance than cel- _ 
lular-tissue, but otherwise similarly e 
through the tissues of the plant. Ducts are tubes usually of much 
greater diameter and length than the spiral vessel, containing a spiral 
fibre incapable of being unrolled, and often broken into imperfectly rs 
bars, or rings, or dots, or disposed like the rungs of a ladder. ey 
occur chiefly in the wood; are abundant in the wood of ferns; but _ 
absent from the wood of Conifers; their functions are not clearly ascer- — 
tained 
laticiferous-tissue, or cinenchyma, consists of uninterrupted, anastomosing, 
thick-walled tubes, which contain a peculiar fiuid called the latex, usually 
turbid ; often coloured red, white, or yellow, but often colourless, The 
use of this tissue is unknown. eo ea ac wees 
