I 



THE CELL- WALL. 



31 



that it consists of solid micellae of definite form, each of which is surrounded by an en- 

 velope of water, and is thus separated from the adjoining micellae ; the more watery a 

 cell-wall-layer, the smaller, according to the principles laid down by Nageli ^, are the solid 

 micellas, the more numerous and the thicker their aqueous envelopes. From this it 

 follows that a certain quantity of water is as indispensable to the growth and to the in- 

 ternal organisation of the cell-wall as is cellulose itself. This water may be designated 

 (water of organisation^ in the same sense as we speak of ' water of crystallisation ; * and as 

 the latter is indispensable to the formation of many crystals, so is the former to the 

 structure of the cell-wall. It is moreover, as we shall see, a peculiarity of all organised 

 structures to contain this water of organisation, at least as long as they continue to grow, 

 because they all alike grow by intussusception. 



From what has been said it will easily be seen that the concentric formation of 

 layers of a cell-wall growing by intussusception differs essentially from the repeated 



FIG. 33.— Macrospores oi Pilidarta globttlifera, in optical longitudinal section; A a still unripe spore, in 

 which the outermost gelatinous layer of the cell-wall is still wanting, though present in the ri^e spore B ; the two 

 outermost layers of the cell-wall of the latter (c and d) have assumed a prismatic structure, especially in c ; in a? 

 stratification is feebly indicated at the same time. Seen from the surface the prisms appear like areola;. The 

 bounding-surfaces of the prisms are, in the corresponding cell- wall layer oi Marsilia Salvatrix, more solid and 

 cuticularised, by which the appearance of a honey-comb is produced. (The layers b, c, and d together form the 

 epispore.) (See also Book II., Rhizocarpeae.) 



formation of a cell-wall round one and the same protoplasm-mass ; cell-walls enclosed 

 one within another may be produced in this manner; but these cannot be considered as 

 layers of one cell-wall ^. Such a process is very common in the formation of the pollen- 

 grains of Phanerogams; within each of the four cells formed by the division of the 

 mother-cell the protoplasm forms round itself a new cell-wall, before the mother-cell- 

 wall has disappeared (Fig. 34). 



But the renewal of a cell-wall may also be brought about by the internal layers of 

 the cell-wall increasing by intussusception, while the external mass of layers undergoes no 

 further growth. Thus the cell-wall of spores and pollen-grains originally grows as a 



' The theory of the growth of the cell-wall (as of all organised structures) by intussusception 

 was first originated by Nageli in his great work on Starch (1858). Compare also Sachs, Handbuch 

 der Experimental-physiologie der Pflanzen, § 114. 



^ [A striking instance of such a multilaminated cellulose-envelope is afforded in the remarkable 

 organism described by Archer under the name of Chlamydomyxa, Quart. Jour. Micr. Sci. 1875, 

 p. 129.] 



