THE CULTIVATOR. 
91 
75. The stem of an exogenous plant may therefore be compared to a 
piece oflincn, of which the weft is composed of cellular tissue, and the 
warp of fibrous and vascular tissue. 
76. In the spring and autumn-a viscid substance is secreted between 
the wood and the liber, called the cambium. 
77. This cambium appears to be the matter out of which the cellular 
horizontal substance of the stem is organized. 
78. In endogenous stems the portion at the circumference is harder 
than that in the centre; and there is no separable bark 
79. Their stems consist of bundles of woody matter, imbedded in cellu¬ 
lar tissue, and composed of vascular tissue surrounded by woody fibre. 
80. The stem is not only the depository of the peculiar secretions of 
species (67.) but it is also the medium through which the sap flows in its 
passage from the roots into the leaves. 
81. In exogenous stems (63.) it certainly rises through the alburnum, 
and descends through the bark. 
82. In endogenous stems (64.) it probably rises through the bundles of 
wood, and descends through the cellular substance; but this is uncertain. 
S3. Stems have the power of propagating an individual only by means 
of their leaf-buds. If destitute of leaf-buds, they have no power of mul¬ 
tiplication, except fortuitously. 
IV. LEAF-BUDS. 
84. Leaf-buds are rudiments of branches, enclosed within scales, which 
are imperfectly formed leaves. 
85. All the leaf-buds upon the same branch are constitutionally and ana¬ 
tomically the same. 
86. They are of two kinds; viz. regular or normal, and adventitious or 
latent, (119.) 
87. Regular leaf-buds are formed at the axillae of leaves. 
88. They are organs capable of propagating the individual from which 
they originate. 
89. They are at first nourished by the fluid lying in the pith, but finally 
establish for themselves a communication with the soil by the woody mat¬ 
ter which they send downwards. 
90. Their force of development will be in proportion to their nourish¬ 
ment; and,-consequently, when it is wished to procure a young shoot of 
unusual vigor, all other shoots in the vi-inity are prevented growing, so 
as to accumulate for one shoot only all the food that would otherwise have 
been consumed by several. 
91. Cutting back to a few eyes is an operation in pruning to produce the 
same effect, by directing the sap, as it ascends, into two or three buds only, 
instead of allowing it to expend itself upon all the others which are cutaway. 
92. When leaf-t>uds grow, they develope in three directions; the one 
horizontal, the other upward, and the third downward. 
93. The horizontal development is confined to the cellular system of the 
bark, pith, and medullary rays. 
94. The upward and downward developments are confined to the woody 
fibre and vascular tissue. 
95. In this Respect they resemble seeds; from which they differ physi¬ 
ologically in propagating the individual, while seeds can only propagate the 
species. 
96. When they disarticulate from the stem that bears them, they are 
called bulbs. 
97. In some plants, a bud, when separated from its stem, will grow and 
form a new plant if placed in circumstances favorable to the pieseivation 
of its vital powers. 
98. But this property seems confined to plants having a firm, woody, 
perennial stem. 
99. Such buds, when detached from their parent stem, send roots down¬ 
wards and a stem upwards. 
100. But if the buds are not separated from the plant to which they, be¬ 
long, the matter they send downwards becomes wood and liber, (66.) and 
the stems they send upwards become branches. Hence it is said that wood 
and liber are formed by the roots of leaf-buds. 
101. If no leaf-buds are called into action, there will be no addition oj 
wood: and consequently, the destruction or absence of leaf-buds is accom¬ 
panied by the absence of wood: as is proved by a shoot, the upper buds of 
which are destroyed and the lower allowed to develope. The lower part 
of the shoot will increase in diameter: the upper will remain of its original 
dimensions. 
102. The quantity of wood, therefore, depends upon the quantity of 
leaf-buds that develope. 
103. It is of the greatest importance to bear this in mind in pruning 
timber trees: for excessive pruning must-necessarily be injurious to the 
quantity of produce. 
104. If a cutting with a leaf-bud on it be placed in circumstances fitted 
to the development of the latter, it will grow and become a new plant. 
105. If this happens when the cutting is inserted in the earth, the new 
plan is said by gardeners, to be upon its own bottom. 
106. But if it happens when the cutting is applied to the dissevered end 
of another individual, called a stock , the roots are insinuated into the tis¬ 
sue ol the stock, and a plant is said to be grafted, the cutting being called 
a scion. 1 
107. There is, therefore, little difference between cuttings and scions, 
except that the former root into the earth, the latter into another plant. 
108. But if a cutting of the same plant without a |eaf-bud upon it be 
placed in the same circumstances, it will not glow but will die. 
109. Unless its vital powers are sufficient to enable it to develope an 
adventitious leaf-bud, (119 ) 
110. A leaf-bud separated from the stem will also become a new indi¬ 
vidual, if its vital energy is sufficiently powerful. 
111. And this, whether it is planted in earth, into which it roots, like 
a cutting, or in a new individual to which it adheres and grows like a scion. 
In the former case it is called an eye, in the latter a bud. 
112. Every leaf-bud has, therefore, its own distinct system of life, and 
of growth. 
113. And as all the leaf-buds of an individual are exactly alike, it follows 
that a plant is a collection of a great number of distinct identical systems 
of life, and consequently a compound individual. 
114. Regular leaf-buds being generated in the axillce of the leaves, it is 
there that they are always to be sought. 
115. And if they cannot be discovered by ocular inspection, it may ne¬ 
vertheless be always inferred with confidence that they exist in such situa¬ 
tions, and may possibly be called from their dormant state into life. 
116. Hence, wherever the scar of a leaf or the remains ot a leaf, can be 
discovered, there it is to be understood that the rudiments exist of a sys¬ 
tem which of life may be, by favorable circumstances, called into action. 
117. Hence, all parts upon which leaves have ever grown may be made 
use of for purposes of propagation. 
118. From these considerations it appears that the most direct analogy 
between the animal and vegetable kingdoms is with the polypes of the 
former. 
119. Adventitious leaf-buds are in all respects like regular leaf-buds, ex¬ 
cept that they are not formed at the axillx of leaves, but develope occa¬ 
sionally from all and any parts ot a i.lant. 
120. They are occasionally produced by roots, by solid wood, or even 
by leaves and flowers. 
121. Hence roots, solid wood, or even leaves and flowers may be used 
as means of propagation 
| 122. But as the development of adventitious buds is extremely 
! uncertain, such means of propagation can never be calculated on ; 
j and form no part of the science of cultivation. 
123. The cause of the formation of adventitious leaf-buds is un¬ 
known. 
| 124. From certain experiments it appears that they may be gene¬ 
rated by sap in a state of great accumulation and activity. 
125. Consequently, whatever tends to the accumulation of sap in 
an active state may be expected to be conducive to the formation of 
adventitious leaf-buds. 
V. LEAVES. 
126. Leaves are expansions of bark, traversed by veins. 
127. The veins consist of spiral vessels enclosed in woody fibre; 
they originate in the medullary sheath and liber; and they are con¬ 
nected by loose parenchyma, [7.] which is full of cavities containing 
air. 
128. This parenchyma consists of two layers, of which the upper 
is composed of cellules perpendicular to the cuticle, and the lower of 
cellules parallel with the cuticle. 
129. These cellules are arranged so as to leave numerous open 
passages among them for the circulation of air in the inside of a leaf. 
Parenchyma of this nature is called cavernous. 
130. Cuticle is formed of one or more layers of depressed cellular 
tissue, which is generally hardened, and always dry and filled with air. 
131. Between many of the cells of the cuticle are placed aper¬ 
tures called stomata, which have the power of opening and closing 
as circumstances may require. 
132. It is by means of this apparatus that leaves elaborate the sap 
which they absorb from the alburnum, converting it into the secre¬ 
tions peculiar to the species. 
133. Their cavernous structure (129) enables them to expose the 
greatest possible surface of their parenchyma to the action of the 
atmosphere. 
134. Their cuticle is a non-conducting skin, which protects them 
from great variations in temperature, and through which gaseous 
matter will pass readily. 
135. Their stomata are pores that are chiefly intended to facili¬ 
tate evaporation ; for which they are well adapted by a power they 
possess of opening or closing as circumstances may require. 
136. They are also intended for facilitating the rapid emission of 
air, when it is necessary that such a function should be performed. 
I 137. The functions of stomata being of such vital importance, it is 
I always advisable to examine them microscopically in cases where 
