26 
INTRODUCTION TO BOTANY. 
ders or cells producing otiuers under the influ- 
ence of the vital principle; and exterior stimu- 
lating influences. It is the knowledge of this 
general principle which so strongly supports 
the doctrine (or, as some say, dogma) of Mor- 
phology. The existing cells develope other 
cells, and thus the plant is extended, but the 
nature of these cells as regards the external 
characters they assume may be varied accord- 
ing to the conditions under which they are 
developed, always providing that there is in 
plants an individuality which restrains the 
variations within certain limits. This kind 
of tissue, the cellular, is found in two essen- 
tially different states, membranous and fibrous. 
Woody tissue is that which forms the bulk 
of the ligneous part of plants ; it consists of 
slender tough membranous tubes, tapering 
towards each end, and lying in compact 
bundles. Vascular tissue, is that of which 
what are called the vessels of plants are com- 
posed, the principal kinds of which are spiral 
vessels— membranous tubes with conical ex- 
tremities, occupied internally by a spiral fibre 
— and ducts, which are thought to be modifi- 
cations of spiral vessels. Luticiferous tissue 
consists of branched anp,stomosing tubes, or 
" milk vessels." Pitted tissue is a modification 
of cellular tissue. 
Within the tissue of plants certain particles 
are found, of which one of the most important 
is starch. To this substance peculiar interest 
attaches, in studying the structure and cha- 
racteristics of plants, inasmuch as it is the ab- 
sence or presence of starch which best distin- 
guishes between animals and plants, as already 
mentioned. We shall therefore quote some 
part of the account given of this secretion : — 
" This substance is so common that no plant 
is destitute of it, and many, like the potato, 
have the cells of their tubers or other parts of 
the stem filled full of its granules. The rhi- 
zome of Equisetum is so crowded with them, 
that when the cells are wounded, the starch 
grains are discharged with some force, appa- 
rently by the contraction of the membrane, so 
that the grains appear as if in voluntary mo- 
tion as long as the emptying the tissue con- 
tinues to take place. These particles are 
perfectly white, semi-transparent, generally 
irregularly-oblong, sometimes compound, and 
marked with oblique concentric circles ; they 
are extremely variable in size, some being as 
fine as the smallest molecular matter in pol- 
len, that is, not more than ^y—o th of an inch 
in diameter, others being as much as ToWl^h 
or —^o^h. * « * StaTch grains of the 
smallest size have a distinct motion of rotation 
when suspended in water, and this motion 
looks as if spontaneous ; for of several floating 
near each other in the same medium, a part 
will be in active motion while others remain 
inactive. Starch when dry is tolerably hard, 
and falls to powder when rubbed between the 
fingers ; when moist it is rather gelatinous ; 
when dried from solution it at first forms a 
trembling jelly, and afterwards becomes vitre- 
ous, brittle, and as clear as water (even in 
lichens) ; when perfectly clean and fresh from 
the plant, starch gradually dissolves in water 
(or only disperses? for the so-called solution 
cannot pass through a cellular membrane); in 
the plant it is usually protected from solution 
by an incrusting wax, albumen,* mucus, or any 
sucii substance outside. Starch is easily (par- 
tially) soluble in boiling water, acids and 
alkalies } insoluble in alcohol, ether, volatile 
or fat oils ; it is stained blue by iodine, even 
in dilute solutions (and the iodide of starch is 
not more soluble in water than ordinary starch, 
but it is insoluble in acids). It appears to be 
changed through intermediate matter; as for 
instance. Lichen starch into Amyloid ; tlirough 
the material discovered by Henry in the mace, 
into membrane, vegetable jelly, and perhaps 
also into gum. The chemical composition of 
starch is now placed beyond doubt by the dis- 
tinguished chemists Berzelius and Liebig, and 
is given thus— C 12, H 20, O 10."— P. 114. 
" Starch is the most common of all vegetable 
productions. I know of no plant that does not 
in some season or other, at least at the time 
when vegetation is at rest, secrete starch in 
more or less abundance; often only in single 
grains in the cells, but often also swelling the 
cells from the large quantity of it. The grains 
of starch adhere to the cell walls, for the most 
part accidentally by means of mucus. The 
supposed bilum by which the grains of starch 
have been said to be held to the sides of the 
cells, is one of Turpin's innumerable careless 
representations, and is entirely without foun- 
dation. The largest starch-grain does not 
appear to be more than 005 of a line in the 
longest part. Starch can generally be sepa- 
rated from the cellular tissue by bruising and 
washing with water ; often, however, it can- 
not, as, for example, when it occurs united to 
mucus, as in Hedychium. Starch seems to 
be purest in Maranta arundinacea. It is not 
too much to say that for two-thirds of man- 
kind, search is the most important if not ex- 
clusive source of nourishment. It is certain 
that starch occurs in all plants, but not always 
in such a state as to suffice and become fit for 
food ; it often cannot be separated from other 
disagreeable substances, as in the horse-chest- 
nut. Certain parts of plants secrete it more 
than others, viz,, the albumen of the seeds 
(Grasses), the cotyledons of the embryo (Le- 
* Used in the sense of Chemists, not of Vegetable 
Physiologists. 
