152 VEGETABLE CELLS. 



by universal expansion and thickening up to a certain 

 point ; the process of formation of membrane then gra- 

 dually changes, and at length ceases. 



The behaviour of the membrane at the apices of grow- 

 ing axes, and below these apices, exhibits exactly the 

 same opposed relation, as the formation of membrane in 

 cell-formation, and the universal growth of membrane 

 after cell-formation. 



The apical growth, therefore, consists not merely of a 

 continuous production of contents, but also of a continuous 

 production of new menibrane at the apex of the axis. 



Many cells with apical growth branch. They deve- 

 lope new branch-cells from their lateral surface, and 

 these elongate by a repetition of the apical growth. Cells, 

 also, which do not grow at the apex themselves, may send 

 out a branch which exhibits apical growth ; thus the cells 

 which grow out into an appendage, as in the cells consti- 

 tuting the articulations of the Confervas, to form a branch- 

 cell or a root ; many cells of young bark or epidermis, to 

 produce a hair or radical fibril; the sporangial cells of 

 Achlya, to discharge the motile cellules (pi. Ill, figs. 4, 

 6, 8), &c. 



The phenomena occurring in these cases, when they 

 can be perfectly seen, as is possible, for instance, in 

 JSryopsis, are as follows : At some point on the surface 

 of the cell, where the branch is to be formed, a little disc 

 of homogeneous mucilage is produced immediately beneath 

 the membrane ; the mucilaginous layer here produces a 

 definite quantity of new mucilage. Then the cell- wall 

 becomes elevated into a little triangular, hemispherical, or 

 conical papilla, filled with homogeneous mucilage. The 

 papilla grows larger. The mucilage becomes granular at 

 the lower part. The granulation of the mucilage advances 

 continually upwards. The formation of chlorophyll, or 

 other colouring matter, and of starch, commences at the 

 base, and also progresses upwards. Then the mucilage 

 at the lower end begins to apply itself upon the walls, 



