INTRODUCTION TO BOTANY. 
31s 
which influences all the phenomena connected 
with the growth of plants, in opposition to 
the views of those m'Iio recognise no such 
principle at work in the vegerable structure, 
but account for all the changes -which take 
phice by the rules of abstract science. A 
living plant, however, is no snch machine 
as this doctrine would seek to make it ; and 
this is forcibly set forth in the following 
paragraphs : — 
'•' I. If we place a seed, (that of an apple 
for instance,) in earth at tlie temperature of 
32° Fahrenheit, it will renidin inactive till it 
finally decays. But if it is ph;ced in moi,-t 
earth some degrees above 32", and screened 
from the action of light, iLs integument gra- 
dually imbibes moisture, and swells ; the 
tissue is softened and acquires the capability 
of stretching ; the water is decomposed, and 
a part of its oxygen combining with the car- 
bon of the seed, forms carbonic acid, which 
is expelled ; nutritious food for the young 
parts is prepared by the conversion of starch 
into sugar ; and the vital action of the embryo 
commences. It lengthens downwards by the 
radicle, and upwards by the cotyledons ; the 
former penetrating the soil, the latter eleva- 
ting themselves above it, acquiring a green 
colour by the decomposition of the carbonic 
acid they absorb from the earth and atmo- 
sphere, and unfolding in the form of two 
opposite roundish leaves. This is the first 
state of vegetation ; the young plant consists of 
little more than cellular tissue ; only an im- 
perfect development of vascular and fibrous 
tissue being discoverable in the form of a sort 
of* cylinder, lying just in the centre. The 
part within the cylinder at its upper end, is 
now the pith, without it the bark, while the 
cylinder itself is the preparation for the medul- 
lary sheath, and consists of vertical tubes pass- 
ing through and separated by cellular tissue. 
" The young root is now lengthening at its 
point, and absorbing from the earth its nutri- 
ment, w'hich passes up to the summit of the 
plant by the cellular substance, and is in part 
impelled into the cotyledons, where it is aera- 
ted and evaporated, but chiefly urged upwards 
against the growing point, or plumule. 
" II. Forced onwards by the current of sap 
which is continually impelled upwards from 
the root, the plumule next ascends in the form 
of a little twig, at the same time sending 
downwards, in the centre of the radicle, the 
earliest portion of wood that is deposited, and 
compelling the root to emit little ramifications ; 
and simultaneously the process of lignifica- 
tion is going on in all the tissue, by the deposit 
of a peculiar secretion in layers within the 
cells and tubes. 
"Previously to the elongation of the plu- 
mule, its point has acquired the rudimentary 
state of a leaf ; this latter continues to develope 
as the plumule elongates, until when the fij-st 
iiiternodeof the latter ceases to lengthen, the 
leaf iias actually arrived at its complete for- 
mation. AYhen fully grown, it repeats in a 
much more perfect manner, the functions 
previously peiformed by the cotyledons ; it 
aerates the sap ibat it receives, and returns 
the superfluous portion of it downwards 
through the liark to the root ; tubular tissue 
at the same time appears between the medul- 
lary sheath and the bark, thus forming the 
first ligneous stratum, a part of which is incor- 
porated with the bark, the remainder forming 
wood. 
'• Daring these operations, while the plumule 
is ascending, its leaf forming and acting, and 
the woody matter created by it descending, 
the cellular tissue of the stem is forming and 
expanding horizontally, to make I'oom for 
the new matter forced into it ; so that develop- 
ment is going on simultaneously both in a 
horizontal and perpendicular direction. This 
process may not inaptly be compared to that 
of weaving, the warp being the perpendicular, 
and the weft the horizontal Ibrmation. In 
order to enable the leaf to perform its func- 
tions of aeration completely, it is traversed by 
veins, originating in the medullary sheath ; 
and has delicate pores {stotn,ates), which com- 
municate with a highly complex pneumatic sys- 
tem, extending to almost every part of the plant. 
" Simultaneously with the appearance of 
woody matter, the emission of young roots, 
and their increase by addition to the cellular 
substance of their points, take place. They 
thus are made to bear something like a defi- 
nite proportion to the leaves they have to sup- 
port, and with which they must of necessity 
be in direct communication. 
"After the production of its first leaf by the 
plumule, others successively appear in a spi- 
ral direction around the axis, at its growing 
point, all constructed alike, connected with 
the stem or axis in the same manner, and per- 
forming precisely the same functions as have 
just been described. At last the axis ceases 
to lengthen ; the old leaves gradually fall off ; 
the new leaves, instead of expanding after their 
formation, retain their rudimentary condition, 
harden and fold over one another, so as to be 
a protection to the delicate point of growth, 
or in other words, become the scales of a bud. 
We have now a shoot with a woody axis, and 
a distinct pith and bark, and of a more or less 
conical figure. At the axil of every leaf a 
new growing point had been generated du- 
ring the growth of the axis, so that the shoot 
when deprived of its leaves is covered from 
end to end with little, symmetrically arranged, 
projecting bodies, which are the buds. 
