THE VEGETABLE CELL. 





membranes on the outside of the primordial utricles during this 

 process, wHch membranes form secondary layers to the parent- 

 cell where in contact with its walls, and laminse of a partition 

 dividing the parent-cell where in contact at the point of junction 

 of the two secondary cells. The number and direction of their 

 septa depend altogether on the number and position of the nuclei, 

 since each of these becomes the centre of a secondary cell. The 

 secondary cells accurately fill the cavity of the parent-cell, so that 

 there is no trace of inter-cellular passages running between them, 

 and the entire contents of the parent-cell are taken into the cavi- 

 ties of the secondary cells. 



Since the membrane of the secondary cells deposited during 

 the formation of the partition is immeasurably thin, wliile the 

 membrane of the parent-cell usually possesses, before the division, 

 a perceptible, often considerable, thickness, we naturally find, on 

 examining a cellular tissue shortly after the division of the cells 

 (fig 48), a very considerable difference in the thickness of the dif- 



Fig. 48 



External layers of the rmd of Cereus peruv2anus —a;, cells of the rmd witli contracted pnmor- 

 dul utricles contracted, m part contammg' newly formed septa (e) 0, Cork-cells , 5, the outer layers of 

 tlie nnd-cells, newly-formed by the division of the latter , c, cells of the epidennig ; d, ctiticle. 



ferent sides of the cells composing it, for some of the walls consist 

 of the blended membranes of the secondary cells, others of these 

 united to the membranes of the parent-cells. This condition is in 

 a high degree striking in the investigation of many organs in 

 V'hich the development has just begun, 6.g., in the formation of a 

 periderm in the outer cells of the bark, where most of the newly- 

 formed and thin septa run parallel with the epidermis; in cam- 



