ELEMENTARY STRUCTURE.—THE CELL. 21 
pericarp, and the seed or seeds contained within it. At vary- 
ing periods, but commonly when the fruit is ripe, the pericarp 
opens so as to allow the seeds to escape; or it remains closed, 
and the seeds can only become free by its decay. Inthe former 
case the fruit is said to be dehiscent ; in the ; 
latter, indehiscent. Fie. 36. 
The seed, as already noticed, is the 
fertilised ovule. It consists essentially of 
two parts ; namely, of a nucleus or kernel 
(fig. 36, emb, alb), and inteywments, int. 
- There are usually two seed-coats or in- 
teguments, the external of which is com- 
monly designated as the testa or episperm, 
and the inner as the tegmen or endoplewra. _. ; ‘ 
The nucleus or kernel may either consist 7, 36. Vertical pirete 
wholly of the embryo, which is alone of Poppy (Papave7). 
essential to it (fig. 16), or of the embryo — i”. Tnteguments. el 
(fig. 36, emb), enclosed in nourishing or endosperm. The 
matter, called the endosperm or albumen, Parts within the inte- 
lb guments form what is 
ial a commonly termed the 
The parts of the embryo having been __ nucleus of the seed. 
already described, we have now finished rue, 
our general sketch of plants in different degrees of organisation, 
together with the compound organs which they respectively 
present, and are, therefore, now able to proceed with the descrip- 
tion in detail of the elementary structures of which they are 
composed. 
CHAPTER 2. 
ELEMENTARY STRUCTURE OF PLANTS, OR VEGETABLE 
HISTOLOGY. 
Section 1. Or THE CELL As AN INDIVIDUAL. 
Tue description of the elementary structure of plants is termed 
Vegetable Histology. 
All the lower kinds of plants, as we have seen (pp. 6-9), 
are made up of one or more membranous closed sacs called cells ; 
and all other plants, however complicated in their appear- 
ance and structure, are also made up of these simple bodies, 
variously modified in form, size, and texture, and in their 
modes of combination, according to the different surrounding 
conditions in which they are placed, and the functions which 
they have to perform (see page 37). The cell is therefore the 
only elementary organ possessed by a plant, and hence neces- 
sarily demands our first and particular attention. We shall begin, 
