28 
INTRODUCTION TO BOTANT. 
the embryo, ami has even been denominated 
a fixed embryo. This comparison must not 
however be understood to indicate any iden- 
tity between these two parts in structure, but 
merely an analogous function, both being 
formed for the purpose of reproduction ; in 
origin and structure they are entirely different. 
The leaf-bud consists of both vascular and 
cellular tissue, the embryo of cellular tissue 
only : the leaf-bud is produced without fer- 
tilisation ; to the embryo this is essential : 
finally, the leaf-bud perpetuates the individual 
as well as the species ; the embryo continues 
the species and not the individual. 
" The usual or normal situation of leaf-buds 
is in the axil of leaves ; and all departure 
from this position is either irregular or acci- 
dental. Botanists give them the name of 
regular when they are placed in their normal 
station, and they call all others latent or ad- 
ventitious. The latter have been found in 
almost every part of plants ; the roots, the 
internodes, the petiole, the leaf, the flower 
itself, have all been remarked producing them. 
" On the leaf they usually proceed from the 
margin, as in Malaxis paludosa, where they 
form minute granulations, first determined to 
be buds by Henslow, or as in Bryophyllum 
oalycinum, and Tellima grandiflora ; but they 
have been seen by Turpi n proceeding from 
the surface of the leaf of Ornithogalum. 
" M. Naudin, in the Annates des Sciences 
Nat., vol. xiv. p. 14, describes some small 
plants of Drosera anglica, which were pro- 
duced on a leaf, on the upper side. They 
sprang from the cellular tissue, between the 
midrib and lateral veins near the edge, and 
were stationed about a line and a half apart. 
They were from five to six lines in length, 
and had, it would seem, a stem with alternate 
leaves, notwithstanding that the Drosera in 
its natural state is stemless, and only provided 
with root leaves. Nothing could be observed 
on the under side of the parent leaf, except a 
black spot below one of the two stems ; there 
were no roots. The stems issued from the 
naked cellular tissue, and had no connexion 
with the vessels of the leaf. This is un- 
doubtedly an universal rule ; burls, whether 
normal, latent, or adventitious, being inva- 
riably formed by exciting the peculiar vitality 
of true cells, and not of tubular forms of 
tissue ; a very important physiological truth. 
" We are unacquainted with the cause of the 
formation of leaf-buds ; all we know is, that 
they proceed exclusively from cellular tissue ; 
and if produced on the axis, from the mouths 
of medullary rays, it would seem as if cer- 
tain unknown forces were occasionally so 
exerted upon a vesicle of cellular tissue, as to 
stimulate it into a preternatural degree of 
activity, the result of which is the production 
of vessels and the formation of a centre, having 
the power of lengthening. Any cellular mat- 
ter, which is not of a perishable nature, may 
be compelled to form buds by a skilful appli- 
cation of heat, moisture, and light. Hence, 
any firm fleshy parts of plants may be em- 
ployed for propagation, especially fragments 
of the root, a part which usually possesses an 
unusually high degree of vitality. A case of 
the artificial compulsory formation of buds by 
the scales of a Hyacinth bulb, is mentioned in 
my Elements of Botany, p. 41. 
" There is indeed an opinion, which I be- 
lieve was that of Mr. Knight, that the sap 
itself can at any time generate buds without 
any previously formed rudiment ; and that 
buds depend not upon a specific alteration of 
the arrangement of the cellular system, called 
into action by particular circumstances, but 
upon a state of the sap favourable to their 
creation. In proof of this it has been said, 
that if a bud of the Prunus pseudo-cerasus, or 
Chinese cherry, be inserted upon a cherry 
stock, it will grow freely, and after a time 
will emit small roots from just above its union 
with the stock ; at the time when these little 
roots are formed, let the shoot be cut back to 
within a short distance of the stock, and the 
little roots will then, in consequence of the 
great impulsion of sap into them, become 
branches emitting leaves. 
" The leaf-buds of the deciduous trees of cold 
climates are covered by scales, which are also 
called tegmenta, or sometimes perulce ; these 
afford protection against cold and external 
accidents, and vary much in texture, thickness, 
and other characters. Thus in the beech, the 
scales are thin, smooth, and dry ; in many 
willows they are covered with a thick down ; 
in Populus balsamifera they exude a tenacious 
viscid juice. In herbaceous plants and trees 
of climates in which vegetation is not exposed 
to severe cold, the leaf-buds have no dead 
scales ; which is also, but very rarely, the case 
in somenorthern shrubs, as RhamnusFrangula. 
" The scales of the bud, however dissimilar 
in their ordinary appearance they may be to 
leaves, are nevertheless in reality leaves in an 
imperfectly formed state. They are the last 
leaves of the season, developed at a period 
when the current of vegetation is stopping, 
and when the vital powers have become almost 
torpid. That such is their nature is suf- 
ficiently shown by that gradual transition 
from scales to perfect leaves, which occurs in 
such plants as Viburnum prunifolium, Mag- 
nolia acuminata, Liriodendron tulipifera, and 
JEsculus pavia : in the latter, the transition 
is perhaps most satisfactorily manifested. In 
this plant the scales on the outside are short, 
hard, dry, and brown ; those next them are 
longer, greenish, and delicate ; within these 
