Development, and Structure of the Vegetable Cell. 411 



although at first slowly and in an altered form ; for from it, just 

 as from a germ-cellj a perfect individual is produced. 



The first perceptible change in the cell is a state of tension of 

 each of its free transverse walls or septa. These transverse 

 septa present, in the normal uninjured state of the Conferva, a 

 flat disk ; but after the section of the neighbouring cells, they 

 become somewhat expanded and pressed outwards from the ends 

 of the uncut cell, so that they present a concavity towards the 

 interior of this cell (PL VI. figs. 30, 31). 



This extension, which is at first exerted equally on both walls, 

 soon acts only upon one of them, and this is always the one 

 which is naturally the lower one — a circumstance which can be 

 best verified in such sections as have a cell branching from 

 them (figs. 30, 31, 43). The enlarging uninjured cell now 

 usually first of all pushes the original lower septum further down- 

 wards, within the cut cylindrical lateral wall, the diameter of this 

 cylinder being generally not entirely occupied, by which circum- 

 stance the progress of the enlarged transverse septum may be 

 distinguished far downwards. This inferior prolongation of the 

 cell gradually becomes smaller in diameter and thinner than 

 its upper portion (figs. 33, 34, 35), and it is also frequently not 

 so thickly occupied with chlorophyll (figs. 42, 45) as are the 

 normal joint-cells of the plant. At the same time the inferior 

 extremity of this prolongation usually afiixes itself to some dead 

 or living organic body, it may be to a living cell of its own spe- 

 cies, extends itself upon this in thin ramifications, and adheres 

 closely to it (PI. VI. figs. 43, 44, 45), by becoming intimately 

 amalgamated, without, however, exerting any perceptible influ- 

 ence upon its vital activity. This direct inferior prolongation 

 of the Conferva-cell thus becomes its radical extremity. 



The upper end of the same cell follows an entirely different 

 course. At first, indeed, the septum exhibits a certain degree 

 of extension like the lower one, but I have never distinctly made 

 out a direct elongation of the apex of the cell upwards into the 

 empty cell above ; but when an act of growth is estabhshed in 

 the upper extremity of the cell (an event commonly subsequent 

 to the extension of the lower end), this expends itself laterally 

 below the transverse septum so as to produce a branch, — the 

 proceeding resembling that whereby ramifications ai'e normally 

 produced in uninjured Confervse. 



The branch therefore is developed within and under cover of 

 the original enveloping membrane of the entire plant, whilst, on 

 the contrary, the organ which represents the root of the higher 

 plants is not covered by this general integument, but, so soon as 

 it has emerged from the surrounding walls of the cut cell, con- 

 tinues to elongate itself in the water quite free and unclothed. 



27* 



