376 Vegetahle Pliysiology. 



Tlie great number of distinct parts, the manifold difference of 

 texture, provision for long duration, &c., involved in the existence 

 of flowers, seeds, and fruits of almost endless variety of character, 

 give occasion, as must be evident, to very great multiformity in 

 the conditions of the fully-developed tissues in the highest class 

 of plants. Among these there are some far more important than 

 others in reference to their connexion with peculiarities in the 

 processes of cell life ; and we shall select for consideration here 

 only those principal forms of the fully-developed cell, with which 

 it is indispensable for the vegetable physiologist to be intimately 

 acquainted. We hope hereafter to be enabled to illustrate the 

 general physiological anatomy of tlie organs of vegetation and 

 reproduction, in a history of the development of the most im- 

 portant agricultural plants. 



As the cells of all plants originate in a similar manner, and 

 are essentially alike in their earliest stages of growth, young 

 organs of plants, and their r/roioiiif/ points or regions, are univer- 

 sally composed of a similar tissue, which may be termed nascent 

 or canilnal tissue, constituting as it were the raw material out 

 of which all the special tissues are developed. The cambial 

 tissue, as found in the apex of buds and roots, in the growing 

 regions of stems and other organs, consists of a closely-packed 

 mass of delicate membranous cells gorged with nitrogenous for- 

 „.^ matlve matters (fig. 1), and, 



according to circumstances, with 

 or without starch, chlorophyll, 

 or other assimilated matters 

 and products intermixed with 

 them. Cells in this condition 

 carry on the development of the 

 ' Y 'fp^'^'"" plant by repetitions of the pro- 



„ ,. , ^ ^ , , ., ,, ,, cess of celt-division, described 



Section of the border of a nascent leaf from the . t* / i 



centre of the hud of the cahl.age. The cell- m OUT former 1 aper (voi. XVll, 

 walls are scarcely visible until iodine is applied, i-q QA\ A fU 11 f 



which coagulates the protoplasmic contents and PP* ' *^} oyjp xi.S ttie Cei»S CI 



causes them to contract and leave the walls, ^^e Cambium - tisSUe multiply, 

 Magnified 400 diameters. , . \ "^ 



the structure increases in size ; 

 and in order that a definite form should be given to the pro- 

 duct, tlie cell-development takes place only in certain definite 

 directions. Thus the formative energy is carried onwards 

 with the advancing points of growth, and the tissue which it 

 leaves behind constitutes the substance of the new organs. In 

 the bud of a palm-tree, for example, the summit is occupied by 

 a mass of cambial tissue, in which the cells continually multiply, 

 advancing the growing point, and leaving behind tliem the cel- 

 lular substance forming the body of the trunk, togetlicr with the 

 lateral mnss-s thrown out from time to time to form the leaves, 



