CHAPTER III 



GROUPS OF TISSUES, OR TISSUE SYSTEMS 



HISTOLOGY 



55. In the lower plants, where all cells are essentially 

 alike and no distinction of tissues can be made, we often 

 find that growth takes place in all parts of the plant, al- 

 most every cell being capable of growth and division at 

 any age. In many plants, however, in which the differ- 

 entiation into various kinds of tissues is still almost lack- 

 ing, we find that growth is more or less limited to certain 

 regions of the plant. In those plants where the tissue 

 differentiation is strongly marked, we find that the 

 formation of new parts, as well as growth, is localized 

 in groups of meristem cells at the apices of stems and 

 roots (and also in many plants at the nodes), the older 

 cells of these groups gradually changing into the more 

 permanent tissues of the plant. 



56. In many seaweeds and fungi, where the plant 

 body consists of separate or adjacent rows of cells, the 

 terminal cell of each row elongates and divides by a 

 cross partition and perhaps division occurs in one or two 

 cells behind it. Except for the formation of branches, 

 longitudinal divisions may be lacking and the result is 

 only the formation of rows of cells. 



57. In the plants which are not so markedly fila- 

 mentous in structure the new tissue at the apex may arise 

 by the division of a single apical cell. This division 

 may be by horizontal partitions, the segments thus 



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