26 COMPENDIUM OF GENERAL BOTANY. 



A. INTERNAL STRUCTURE AND METHOD OF GROWTH OF THE 



CELL-WALL. 



The mature cell-wall shows two internal forms of structure, 

 stratification and striation. Both, in so far as they may be included 

 here, 1 are usually the result of the deposition of layers containing 

 successively more and less water, or (in stratification) they may 

 sometimes be due to chemical differences in the substances. In 

 stratification we are concerned with concentric layers which extend 

 parallel to the surface of the cell-wall ; in striation, with lamellae 

 which usually extend radially. Viewed from the outside these stria- 

 tions seem to extend either diagonally or at right angles to the cell- 

 surface. The cell-wall may consist of longitudinal, spiral, or annular 

 lamellae, and these rings may be placed diagonally or horizon- 

 tally. 



The upper end of Fig. 11, B, shows the spiral striations of a cell 

 cut across. The lamellae seem to be radially placed ; the lower end 

 B shows the diagonal course of the striation when 

 viewed from the inner surface. Stratification 

 and striation mark the cell-wall into numer- 

 ous delicate divisions. The various layers or 

 complexes of layers are sometimes so com- 

 bined in the same cell as to cause striation 

 in various directions. That the difference in 

 F n the amount of water present is the cause of 



A, lameiiation of ceil- stratification and striation is denied by some 



membrane; B, stratification ., m, , u . , . .-, ., . , 



of ceii-membrane. authors. These authors maintain that thick- 



enings in the cell-wall produce striation and that "contact lines" 

 cause stratification and striation. We will, however, follow CORRENS,* 

 who has made a critical study of this subject and more recently 

 has verified his former opinions. According to this author strati- 

 fication and striation (in the true sense) are usually due to water 

 differences, and sometimes to chemical differences in cell-wall sub- 

 stances (having different refractive indices). The same questions 



1 Delicate spiral thickenings, as they occur in cells of conifers, and membrane 

 foldings which produce longitudinal striation in certain epidermal cells, do not 

 belong to these internal structural changes. 



2 CORRENS, who should perhaps be considered the last pupil of NAGELI, wrote: 

 "Zur Kenntnis der innern Struktur der veg. Zellmembranen." Pringsheim's 

 Jahrbucher, XXIII (1891). 



