GROWTH OF CELLS. 149 



their periphery. The cell often becomes twenty to forty 

 times longer than it was at first. The cell is exposed 

 by all its surface, except the base, to the air ; it acquires 

 its fluid nutriment solely through the basilar surface. 

 If the membrane were principally nourished by the pas- 

 sage of nutrient matter through it, the basilar surface 

 alone would be much expanded. Now, since the nucleus 

 exists in the earliest condition, and since normally it is 

 not moveable on account of its lateral attachment, it 

 must, if the theory were correct, lie normally near the 

 apex of the enlarged cylindrical cell, from the growth of 

 the membrane at the base. But it lies, without distinc- 

 tion, sometimes at the apex, sometimes in the middle, and 

 sometimes at the base of the cell. 



Observations on elongated cells, or vessels with spiral, 

 annular, or porous lignification, afford me similar results. 

 If such cells or vessels grow after the lignification has 

 become evident, the spiral fibres, the rings, or pores, 

 separate uniformly on the whole of the lateral surfaces ; 

 the best proof that such elongated cells or vessels expand 

 at their lateral faces, and not at their terminal faces, 

 where the current of sap passes through the membrane. 



The question still remains of the behaviour of the 

 stellate or spongiform cells. They are at first parenchy- 

 matous, but by the secretion of air become separated 

 from each other in the greatest part of the surface, re- 

 maining united together only in places. At the points 

 of contact the cells elongate radially. Schleiden calls 

 this a " growing-out " (Auswachseri) . I see nothing in 

 it but a mechanical drawing-out of those places which 

 cannot separate from the other cells, through the air 

 which has been excreted. The growth of the cells is a 

 different and much more independent process, while the 

 radiating elongation of the stellate and spongiform cells 

 stands in direct relation to the quantity of air secreted. 

 The undulated and dentate epidermal cells, however, 

 which are dove-tailed into one another, and which 

 Schleiden also cites, prove in any case nothing for his 



