1838] 



FARMERS' REGISTER 



583 



61. Some stems are developeil underrrrounil, 

 6tich as the Tuliers of the Poialo iiml the Corums 

 of the Corcup; but they are kiiovvii Irom roots hy 

 the presence ol' leaves, and regular leal-buds upon 

 their snrliice. 



62. Sumus increase in diameter in two ways. 



63. Eiihcr by the addiiion ol' new matter to the 

 outside of the wood and the inside of the bark; 

 when they are Exoi^enous; example, Oak. 



64. Or by the addiiion of new matter to their 

 inside; when \\\ey nw lundogenous ; e.x. Cane. 



65. In E.xoixenous steins, the central portion, 

 which is hanler and darker than that at the cir- 

 cumlerence, is called Heart-wood; while the ex- 

 terior, which is softer and lighter, is calleJ Albur- 

 num, or Sapwood. 



66. The inside of the bark of such stems has 

 also the technical name of Liber. 



67. The Heart-wood was, when young, Albur- 

 num, and atierwards changed its nature, by be- 

 coming the receptacle of certain secretions pecu- 

 liar to the species. 



6S. Hence the greater durability of Heart- wood 

 than of Sap-wood. While the latter is newly 

 formed euipty tissue, almost as perishable as bark 

 itself, the tbrmer is protected against desiruction 

 bp the introduction of secretions that become solid 

 ma'ter, which is olten insoluble in water and never 

 permeable to air. 



69. The secretions by which Heart-wood is so- 

 lidified are prepared in the leaves, whence they 

 are sent downwards through the bark, and from 

 the bark communicaLed to the central part of the 

 stem. 



70. The channels throuffh which this commu- 

 nication takes place are called Medullary Bays, or 

 Silver Grains. 



71. Medullary rays are plates of cellular tissue, 

 in a very compressed state, passing from the pith 

 into the bark. 



72. The wood itself is composed of tubes, con- 

 sisting of woody fibre and vascular tissue, imbed- 

 ded longitudinally in cellular substance. 



73. This cellular substance only developes hori- 

 zontally; and it is to it that the peculiar character 

 of different kinds of wood is chiefly due. 



74. For this reason the wood of the stock of a 

 grafted plant will never become like that of its 

 scion, although as will be hereafter seen (iv.), the 

 woody matter of the stock must all originate in 

 the scion. 



75. The stem of an exogenous plant may there- 

 fore be compared to a piece of linen, of which the 

 Ave ft 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 sterns the portion at the 

 •circumference is harder than that in the centre; 

 and there is no separable bark. 



79. Tneir stems consist of bundles of woody 

 matter, imbedded in cellular tissue, and composed 

 of vascular tissue surrounded by woody fibre. 



80- The stem is not only the depository of the 

 peculiar secretions of spocies ("67.), but is also the 

 medium through which the sap flows in its pas- 

 sage from the roote into the leaves. 



81. In P^xogiMious stems (63.) it certainly rises 

 through the alburnum, and desccuds through the 

 bark.' 



82. In Endnijrnoua stems (64.) it probably 

 rises IhrouL'h the bntidlcs of wood, ;u)d descends 

 through the cellular substance; but this is uncer- 

 tain. 



83. Stems iiave the power of propagating an 

 individual only by the means of the Leal-buds. 

 If destitute of Leai-linds, they have no power of 

 multiplication, except fortuitously. 



IV. Leaf-Buds. 



84. Leaf-buds are rudiments of branches en- 

 closed within scales, which are imperlectly lurmed 

 leaves. 



85. All the Ieaf-bu(;s upon the same branch are 

 constitutionally and anatomically the same. 



86. They are of two kinds; viz: regular or nor- 

 mal, and adventitious or latent. (119.) 



87. Regular leal-buds are formed at the axillae 

 of Leaves. 



88. They are organs capable of propagating the 

 individual from which they oriixinate. 



89. They are at first nourished by the fluid ly- 

 ing in the pith, but finally established lor them- 

 selves a communication with the soil by the woody 

 matter which they send downwards. 



90. Their Ibrce ol developenient will be in pro- 

 portion to their nourishment; and, consequently, 

 when it is wished to procure a young shoot of un- 

 usual vigor, all other shoots in the vicinity 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 lew e3'es is an operation 

 in pruning to produce the same efiect, by directing 

 the sap, as it ascends, into two or three buds onlv, 

 instead of allowing it to expend itself upon all the 

 others which are cut away. 



92. When leaf-buds grow, they develope in 

 three directions; the one horizontal, the other up- 

 ward, and the third downward. 



93. The horizontal developement is confined to 

 the cellular system of the bark, pith, and medul- 

 lary rays. 



94. The upward and downward developements 

 are confined to the woody fibre and vascular 

 tissue. 



95. In this respect they resemble seeds; from 

 which they difi'er physiologically in propafratin"- 

 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 preservation of 

 its vital powers. 



98- But this property seems confined to plants 

 having a firm, woody perrennial stem. 



99. Such buds when detached from their parent 

 stem, send roots downwards and a stem upwards. 



100. But if the buds are not separated from the 

 plant to which they belong, 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 of wood; and consequently, 



