INTRODUCTION TO BOTANY. XVil 
§ 15. The Seed. - 
_ 138. A seed is the fertilised ovule arrived at maturity. It is almost always, except 
in Conifers, enclosed in the pericarp. It contains, when ripe, an embryo or young 
plant, either filling or nearly filling the cavity, but not attached to the outer shell 
or skin of the seed ; or immersed in, or lying close to, a mealy, horny, oily, or fleshy 
substance, called the albwmen or perisperm. The presence or absence of this albumen, 
that is, the distinction between albuminous and exalbuminous seeds, is one of great 
importance. The embryo or albumen can often only be found or distinguished 
when the seed is quite ripe, or sometimes only when it begins to germinate. 
139. The shell of the seed consists usually of two separable coats. The outer coat, 
called ¢esta, is usually the principal one, and in most cases the only one attended to 
in descriptions. It*may be hard and crustaceous, or thin and membranous, dry, or 
rarely succulent. It is sometimes expanded into wings, or bears a tuft of hair, cotton 
or wool, called a coma. The inner coat is called tegmen. 
140. The fumicle (115) or stalk by which a seed is attached to the placenta, is occa- 
sionally enlarged into a, membranous, pulpy, or fleshy appendage. which sometimes 
almost closes over the seed; this is called an aril. A strophiole or caruncle is a 
similar appendage, originating in the testa, Seeds having an aril are said to be 
arillate. . 
141. The hilum (115) is the scar left on the seed when it separates from the funi- 
ian The micropyle (118) is the mark indicating the position of the foramen of the 
ovule, 
142. The Embryo consists of the radicle or root-stem; one or two cotyledons or 
primary leaves (seed-leaves); and the plumule, or first leaf-bud of the young plant. 
In many seeds, especially when there is no albumen, these several parts are very 
conspicuous ; in others they are difficult to distinguish ; and in some cases the em- 
bryo cannot be found until the seed begins to germinate. 
143. The micropyle (141) always indicates the position of the extremity of the 
radicle, whose direction, either as respects the fruit or the seed, it is often important 
to notice. The Space is said to be e vee 
superior, if pointing towards the summit e fruit. 
inferior, if pointing towards the base of the fruit. 
§ 16. Accessory Organs. 
146. Thorns and Prickles. 
with the woody system of a plant. A p 
from the epidermis or outer skin ; it is not connected with the woody system, and 
147. Hairs, in the general sense, or the indument (or clothing) of a plant include 
all those processes from the epidermis which have been called bristles, hairs, down, 
eotton, or wool. 
The epidermis or surface is said to be 
smooth or even vont when seri any es omer whatever. 
glabrous, when without any hairs of any kind. ee ig 
striate, when marked with rallel re either slightly raised or merely = 
coloured. are aoe 
furrowed or ribbed, when the parallel lines are more distinctly raised. ; 
