OUTLINES OF BOTANY. LXIII 
in the —_ of slegree is very saint being often a mere question of 
convenie The e subdivi 8 upon correct principles are multiplied, 
the more aes facilitate the i age of plants, provided always the main 
resting-points for constant use, the Order and the pag are comprehensive 
and distinct. But if every group i into which a genu peg ml divided be 
— _ a distinct genus, with a substantive aie ‘e membered 
when a species is spoken of, all the advantages derived Go the 
heautifal, aimplicity, of the Linnaean nomenclature are 
The definitio ‘gs above given of Varieties, Races, a y pore , etc., 
must be taken a general Sites as the ‘distinctions between aie are 
not always so aan as they were once thought to be. 
Cuap. II. Veaeraste ANATOMY AND PuysroLoey. 
§$ 1. Structure and Growth of the Elementary Tissues. 
186. If a very thin slice of any part of a plant be placed under a mi- 
croscope of high magnifying power, it will be found to be made up of 
variously shaped and arranged ultimate parts, forming a sort of honeycombed 
structure. These ultimate parts are called cells, and form by their combi- 
nation the elementary tissues of w the entire plant is co 
187 its simplest state is a clos mbranous sac, formed 
re) nce permeable by fluids, gh usually des of bl 
e 
acting, though cohering with the cells with which it is in 
Bae — g¢ of the common life and action of the tissue of which it forms 
7 e membranes separating or enclosing the cells are also called 
their walls 
otanists usually distinguish the following tissues 
a Cellular tissue, or parenchyma, consists usually ot thin- walled cells, 
heir 
more or less round i in form, or with their length not muc 
their breadth, and not tapering at the ends. All the oft p th 
leaves, the pith of stems, the pulp of fruits, and all young growing parts, 
f it. is th first Peary ay s 
ant 
(2) faa y tissue, or pr pein Rosia in having its cells consider- 
ably longer than broad, usually tapering at each end into points an 
overlapping each other. The ¢ ells ae commonly thick: walled; the tissue 
is firm, tenacious, and elastic, and conatiiates the principal part of wood, 
of the inner bark, and of the nerves and veins of leaves, forming, in 
ee 
(3) Vascular tissue, or the vessels or ducts of plants, so called from the 
mistaken notion that their hncticns are analogous to a 3 Aue the vessels 
ies) of animals. 
tube. la: erns 
and a few other cryptogamous plants, have vessels, and are therefore 
called rules plants; so the majority of cryptogams having only cellular 
