360 



THE MICROSCOPE AND ITS REVELATIONS. 



FIG. 241. 



within another (Fig. 241, A), which present themselves as concentric 

 rings when the cells containing them are cut through; and these layers 

 are sometimes so thick and numerous as almost to obliterate the origi- 

 nal cavity of the cell. By a continuance of the same arrangement as that 

 which shows itself in the single layer of the dotted cell each deposit 

 being deficient at certain points and these points corresponding with 



each other in the successive layers 

 a series of passages is left, by which 

 the cavity of the cell is extended at 

 some points to its membranous wall; 

 and it commonly happens that the 

 points at which the deposit is want- 

 ing on the walls of the contiguous 

 cells, are coincident, so that the mem- 

 branous partition is the only obstacle 

 to the communication between their 

 cavities (Figs. 241-243). It is of 

 such tissue that the ' stones ' of stone- 

 fruit, the gritty substance which 

 surrounds the seeds and forms little 

 hard points in the fleshy substance 

 of the Pear, the shell of the Cocoa- 

 nut, and the albumen of the seed 

 of Phyteleplias (known as ( vegetable 



ivory'), are made up; and we see the use of this very curious arrange- 

 ment, in permitting the cells, even after they have attained a consider- 

 able degree of consolidation, still to remain permeable to the fluid re- 

 quired for the nutrition of the parts which such tissue incloses and 

 protects. 



FIG, 242. 



Tissue of the Testa or Seed -coat of a Star- 

 Anise : A, as seen in section: B, as seen on the 

 surface. 



Section of Cherry-stone, cutting 

 the cells transversely. 



Section of Coquilla-nut, in the 

 direction of the long diameters 

 of the cells. 



357. The deposit sometimes assumes, however, the form of definite 

 fibres, which lie coiled-up in the interior of cells, so as to form a single, 

 a double, or even a triple or quadruple spire (Fig. 244). Such spiral 

 cells are found most abundantly in the leaves of certain Orchideous 



