150 VEGETABLE CELLS. 



theory, because a membranous surface, which is uniformly 

 bounded at all points by another surface of membrane, 

 must exhibit like behaviour at all points in reference to 

 nutrition and expansion. 



From the facts here brought forward, I deduce the 

 conclusion, that the cell-membrane normally expands less 

 in those places ivhere it serves for the reception and 

 emission of the nutrient matters, or where it officiates in 

 an interchange of substances or a current of sap ; that, 

 on the other hand, it normally expands more at those 

 places where it has little or no nutrient matter to manage. 



The apical growth is altogether different from the 

 universal growth of cell-membrane. In an earlier me- 

 moir on Caulerpa* I have pointed out this apical growth, 

 and discussed its characters at length.f The apical 

 growths may be observed most easily in the filiform, 

 branched, single-celled Algae and Fungi, as in Caulerpa, 

 Bryopsis, Achlya, &c. The lower part of the cell is 

 quite perfect ; little or no change occurs in the contents ; 

 the cavity is filled with clear, colourless fluid, and on the 

 wall lies the mucilaginous layer, with the chlorophyll- 

 and starch-globules : the membrane expands little or no 

 more. Toward the extremity the membrane becomes 

 thinner ; it is there that new contents and new membrane 

 are formed. 



Immediately below the growing point lies a layer 

 or small disc of homogeneous mucilage. Below, this 

 passes into granular mucilage. To this follows a mass of 

 granular mucilage, in which originate starch, chlorophyll, 

 or other colouring matters. Still lower down, the solid 

 contents are deposited upon the walls. 



* Schleiden und Nageli, Zeitsclir. f. wiss. Bot., Heft i, p. 134. 



f Schleiden (Grundz. d. w. Bot. 3d ed. i, p. 212) confounds the apical 

 growth with the unilateral expansion of universal growth. It is by no means 

 clear to me how he imagines Caulerpa to be " a body which at least appears 

 like a single cell;" further, how " the most decisive proof" of anything can 

 be deduced from this appearance. That Caulerpa actually is a single cell, 

 follows, in my opinion, both from the researches I have published and from 

 its relationship to Bryopsis } Valonia, Codium, Halymeda, Udotea, Faucheria, &c. 



