23] 



CHAPTER I. THE CELL. 



FIG. 45. A cell with 

 pitted walls, from the 

 wood of the Elder (Satn- 

 bucus). A longitudinal 

 section showing the pits 

 in tbe lateral walls as 

 channels, a; and in the 

 farther wall as roundish 

 spots, b. ( x 240.) 



FIG. 48. Transverse sec- 

 tion of a bast-cell from the 

 root of DaJiU'a arinbi!is (x 

 800); I the cell-cavity ; A' pit- 

 canals which penetrate the 

 stratification ; sp a crack by 

 which an inner system of 

 layers has become separa- 

 ted. (After Sachs.) 



Fio. 47. Cells from the endo- 

 sperm of OrnitJwgalum tunbella- 

 tum showing simple pits : 

 m pits seen in surface view ; p 

 closing membrane seen in lon- 

 gitudinal section ; nucleus. 

 (x2X): after Strasburger.) 



ting the thickness of the wall, and these seem in the surface-view 

 to cross each other (Fig. 50). The cause of striation appears to be 

 this, that when a considerable area of cell-wall has to be formed, 

 it is deposited by the protoplasm not as one continuous sheet, but 



FIG. 49. Oval bordered pits in the 

 wall of a vessel of Helianthus. A In 

 longitudinal section. B As seen from 

 the surface ; t the pit ; h the pit-chamber. 

 (x 600). 



FIG. 49. Circular bordered pits on 

 the wood-cells of the Pine. A Seen from 

 the surface. B In section ; s the closing 

 membrane ; m the middle lamella. C An 

 earlier stage, in section. ( x SOO.diagram.) 



