LIFE OF THE PLANT-CELL. Ill 



the different vital properties of the individual cells are exhibited 

 in the varying mode and rapidity with which the cells themselves 

 are perfected. 



It can only be regarded as a law having an average or general appli- 

 cation, that the cells of an entire tissue have identical functions ; and 

 such important exceptions exist in this respect, that the classification of 

 the tissues, according to supposed differences in their functions, appears 

 to be at least wholly untenable ; the morphology of the cell alone afford- 

 ing a sufficient principle to go upon. In the same parenchyma we find 

 a cell crammed full of starch, next to a similar one containing nothing 

 but essential oil ; and both, probably, contiguous to a third, filled with a 

 clear, watery, red or blue coloured matter ; whilst a fourth, together with 

 various assimilated substances, contains a large quantity of chlorophyll. 

 In the midst of the thin-walled parenchyma we observe scattered, or 

 forming groups with the others, cells of the same size and form, but 

 filled up almost to the closure of their cavity by deposit-layers, as in 

 the so-called stony concretions in the quince and pear, in the bark and 

 pith of Hoja carnosa, and of many trees, in the aerial roots of the 

 Maxillarice, and in a hundred other situations. All this indicates the 

 great independence of the individual cells, and the possibility of each 

 cell, in any situation, on occasion, going through all the phases of cell- 

 life, and becoming developed in any way that the circumstances under 

 which it is placed render necessary. The cell-life is modified only to 

 a slight degree by the mode of disposition of the cells, and consequent 

 dependence on the contiguous cells. Leaving this independence out of 

 the question, the tissues, as a whole, present certain phenomena which 

 must be regarded as peculiar to each. 



58. The cells of the parenchyma enjoy the greatest degree of 

 independence, and it is, consequently, in that tissue that we find, 

 in the greatest number and disposed with the least regularity, cells 

 with the greatest variety of contents, and having the most various con- 

 figuration of their walls, next to each other. Larger masses of the 

 parenchyma present, in preponderating quantity, starch (potato), or 

 fixed oil (cotyledons of the species of Brassica), or gum (roots of 

 Althcea), or emulsin (oil and vegetable albumen in the cotyledons 

 of the almond), or assimilated substances and chlorophyll (in all 

 green leaves), or colouring matters of the same kind (in the petals 

 of flowers), or air (in the pith), &c. 



59. The various formations in the system of intercellular spaces 

 comprehend a very great variety of substances. The peculiarity in 

 this case consists in the circumstance, as I believe, that all the cells 

 forming the boundaries of these intercellular spaces, without excep- 

 tion, exhibit equal vital activity ; they either exert no influence at all 

 upon the contents of the intercellular spaces, or all secrete into it 

 the same material. To this system are to be referred all the various 

 reservoirs of special secretions, resin- and gum-passages, as well as 

 the receptacles of the milk-sap ; and, besides these, the solid inter- 

 cellular substance (substantia inter 'cellularis), which frequently pre- 

 sents a determinate form, dependent on the neighbouring cells. 



