Secondary Deposit 



19 



(fig. 28). Or else it is deposited as separate rings, when an 

 annular cell is formed (fig. 29). When the thickening is 

 arranged in an irregular manner, producing a perfect network 

 over the wall, the cell is said to be reticulated. 



Fig. 2^.— Transverse section of a cell of 

 the pith of Clevtatis vitalba : p, primary 

 cell wall ; /, innermost thickening layer ; 

 p, pore-canal ; ;', intercellular space. 



Fig. 28.— a spiral cell from 

 a Cactus, Opnntia Tuna, 

 with strongly thickened 

 spiral band. 



Very often there is in the cell a gradual passage from a 

 spiral to an annular or reticulated marking (fig. 31). At other 

 times there is a spiral or reticulate marking in addition to the 



Fig. 30. — Reticulately 

 thickened cell of the 

 Touch-me-not (/?«/«- 

 Hens noli-me-tangere). 



Fig. 31. — Annular cell 

 from an Opnntia- with 

 rings passing over into 

 a spiral band. 



Fig. 29. — Annular cell 

 from Amndo donax, 

 with strongly thickened 

 rings placed at different 

 distances and different 

 angles. 



pits or dots. Such cells as these are known as trachei'des 



(fig. 32). 



Fig. 33 shows another form of thickening, known as scalari- 

 form, or ladder-like. In this case the secondary deposit is 



c 2 



