STRUCTURE OF PLANTS. 323 



Structure of Plants. — The development of cells in plants 

 takes place in all cases in essentially the same way, 

 but the form of the result is subject to a number of im- 

 portant modifications. Most elementary works on Botany 

 enter so fully into this interesting question, that it is quite 

 unnecessary to do more than refer very briefly to the 

 more important structural peculiarities of plants. Cell- 

 division, as we have seen, is the universal formative pro- 

 cess by which vegetative growth is effected, and free-cell- 

 formation occurs only in the production of cells connected 

 with reproduction. In the lower classes of plants, espe- 

 cially in aquatic genera, we can observe the process of cell- 

 division in all its details ; but in the higher, knowledge 

 of this kind is only accessible by dissection. 



As long as the cell retains its primordial utricle, it is 

 capable of producing new cells, and organized forms of 

 assimilated matter, like starch, chlorophyll, &c. in its con- 

 tents. This is the case in all nascent tissues, but it ceases 

 to be so at various periods in different parts of the vege- 

 table organization. In all woody tissues, in all pitted and 

 spiral-fibrous cells it disappears early ; the secondary de- 

 posits of the ligneous character being formed apparently 

 from the watery cell-sap. In herbaceous organs, such as 

 leaves, in the cells of the cellular plants generally, the 

 primordial utricle remains. "This explains why the 

 power to form adventitious buds exists not only in the 

 cambrium layer of the higher plants, but, under certain 

 conditions, even in the leaves, and why germination or 

 propagation by little cellular bulbels, or isolated cells 

 detached from the vegetative organs, is so common among 

 the cellular plants, and in the Mosses and Liverworts, 

 where parenchymatous tissues so greatly predominate." — 

 (Henfrey.) 



The tissues of plants, properly so called, consist of col- 

 lections of cells of uniform character, permanently combined 

 together by more or less complete union of their outer sur- 

 faces. Tissues are of many kinds, according to the form 

 of the cells, the character of the cell-membrane, and the 

 manner in which the cells are connected together. The 

 milk- vessels found in connexion with certain cells appear 

 to be formed out of the intercellular passages, and not by 



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