CELLULAR TISSUE. 



13 



g. 34. Beautiful thick wall-cells 

 from the seed of the IlUcium ani- 

 satum, or star-anise, showing the 

 concentric layers, central cavity, 

 and radii. 



t 



Fig. 35. 



A, a mass of thick wall- cells from 

 the PEAK, known as the gritty 

 tissue. 



B, a cell more highly magnified. 



the cavity of the cell is nearly filled. There is, however, always a central vacuity, 



and this is in direct connexion with the cell-wall 



by a series of canals, which pass through the various 



layers of hard tissue. This is absolutely necessary, 



since all actions proceeding in the cell must require 



the direct communication of the cell- wall. 



The thick- walled cells constitute the gritty tissue 



of the pear (Fig.3o) 



a tissue found in 



the form of small 



hard grains near to 



the centre of the 



fruit. It is also 



abundant in the 



so-called bulbs of 



many orchids, as the 



Mirchantia poly- 



morpha ; on the 



covering of the seeds 



of many plants, as 



of the star - anise 



(IlUcium anisatum 



Fig. 34), and the 



apple (malus Fig. 



36) ; in the strong 



part of many nuts, 



as of the ivory nut 



(Figs.37,38),nowso 



usefully supplying 



the place of ivory ; 



in the common haw- 

 thorn ( Cratfeffus") , 



plum, and our garden 



Fitr. 36. Sclerogen immediately in- fruits, and in the 

 eiosing the seed of the apple. C ocoa-nutshell(Fig. 



39). It is also met 



with in the bark of 



almost all trees, as 



on the beech (Fig. 



39). This structure 



is well seen by cut- 

 ting a thin section, 



and placing it in a 



drop of water in the 



ordinary way ; or. 



Fig. 37. 



b, perpendicular section of the bark 

 of the IVORY NCT (Phytelephus 

 macrocarpa} . 



a, longitudinal section. 



Both show the lines of communica- 

 tion between the centre and the 

 circumference. 



Fig. 38. Transverse section of thick n . ,.-,, -, ' , 

 wall-cells of the IVORY NUT. (Phy- better stlll > "7 P lac ~ 

 telephas macrocarpa). ing it in Canada 



balsam. If the section is too thick it must be ground down on a whetstone, in the 



Fig. 39. Thick wall-cells from the 

 COCOA NUT shell, with their central 

 cavities and communicating tubes. 



