280 



MANUAL OF BOTANY 



the living substance forms round itself. We have in these two 

 parts, one living, the other non-living. All such structures are 

 known as cells. 



When one of these cells has existed for a time, it becomes 

 septated into two by the formation of a partition wall of the 

 same substance as the membrane which clothes it, the septum 

 being formed by the protoplasm just as is the original mem- 

 brane. Usually the two cells arising &om such septation 

 remain connected with each other ; each in turn gives rise 

 to another in the same way, and by the continuation of this 

 process we get a mass, made up of a number of cells. These 

 structural units are not, however, completely distinct, for the 

 protoplasm of each is in connection with that of its neigh- 

 bour by delicate filaments 

 Fig. 610. which penetrate the septa, or 



cell-waUs, so that the living 

 substance of such a mass is or- 

 ganically continuous through- 

 out, being supported by the 

 membranes which it has 

 formed, which constitute in- 

 deed a kind of skeleton. 



A section through such a 

 mass shows the appearance of a 

 number of chambers, each occu ■ 

 pied by a portion of the living 

 substance. It needs a very 

 high magnification to distin- 

 guish the connecting threads or 

 strands, which are of extreme 

 tenuity [figs. 610 and 611). In 

 general, we may say then that a 

 plant is built up of an aggrega- 

 tion of such cells. 



Some plants do not always 

 form the dividing septa, so that 

 in them we have many pieces 

 of protoplasm, or protoplasts, 

 connected closely with one another, and having only a common 

 membrane or cell-wall surrounding the whole. Such a plant- 

 body is called a.'ccenocyte. Others form relatively few septa, so 

 that each division of the plant-body contains many protoplasts. 

 Usually each protoplast occupies a, separate chamber. In the 



Fig. 610. Semi-diagrammatic longitudinal 

 section of an old and stout portion of 

 Cei-amium rubrum, showing continuity 

 between tte protoplasmic contents of 

 the axial or central cells, a, a, at their 

 ends; and laterally with the cortical 

 cells, &, by protoplasmic threads, and 

 also that of the cortical cells inter se by 

 threads radiating from the central mass 

 in each cell. After T. Hick. 



