THE VITAL PROPERTIES OF THE CELL 167 



refractive power (Figs. 71, 72 A and B). However, when the 

 surface is examined, a still more delicate structure can frequently 

 be seen. The cell membrane is faintly striated, looking as though 

 it were composed of a large number of parallel layers ; these are 

 crossed by others running in an opposite direction. They run either 

 longitudinally and transversely that is to say, like rings round 

 the cell or are arranged diagonally to the longitudinal axis of the 

 cell. Nageli and Strasburger hold different opinions concerning 

 the relation of this delicate striation towards the separate cellulose- 

 lamellae. 



Nageli (V. 19) considers that both systems of striation are 

 present in each lamella ; further that, as in starch grains, the 

 lamellae, as well as the intersecting bands, consist of substances 

 alternately rich and poor in water, and hence are alternately dark 

 and light in appearance. In consequence, a lamella is, as it were, 

 divided into squares or rhomboids, like a parquetted floor. "These 

 may assume one of three appearances ; they may consist of sub- 

 stances of greater, of less, or of medium density, according as to 

 whether they occur at the point of intersection of two denser, of 

 two less dense bands, or of one dense and one less dense band." 

 Hence Nageli is of opinion that the whole cell membrane " is 

 divided in three directions into lamellae, which consist of sub- 

 stances alternately rich and poor in water, and which intersect in 

 a manner similar to that seen in the intersecting laminae of a 

 crystal. The laminae in one direction compose the layers, those 

 in the others the two striated systems. These latter may intersect 

 at almost any angle ; they both meet the lamellae of the layers, 

 apparently, in most cases at right angles." 



On the other hand, in opposition to Nageli, Strasburger (V. 

 31-33) and other botanists, whose statements are not to be dis- 

 puted, consider that intersecting strire never belong to the same 

 lamella ; they think it much more likely that if one lamella is 

 striated in a longitudinal direction, the next one is striated trans- 

 versely, and so on alternately. Strasburger does not believe that 

 the difference, either in the lamellae or the striae, is due to the 

 varying amount of water which they contain. The lamella? and 

 the striae in them are separated from one another by their 

 surfaces of contact, which, in consequence of being seen at 

 different angles (cross section and surface view), appear as 

 darker lines. Thus the arrangement is similar, in the main, to 

 that seen in the cornea, which consists of lamina? formed of 



