THE PROTOPLAST AS HOUSE-BUILDER 



61 



True crystals are found in the epidermal cells of the leaf of the Iris and 

 the Fiichsia. In the latter, they are disposed in little bundles, and look like 

 so many broken pieces of needle whence the name raphides (Lat. raphis, 

 a needle) which is sometimes applied to them (fig. 81). Stellate crystals are 

 met with in the bark of the Lime-tree (Tilia) ; cubical in the Onion (Allium) ; 

 and sphere crystals in one of the Stinkhorn Fungi viz. Phallus caninus. 

 A good slide for showing the cubical crystals of the Onion may be made by 

 soaking a little of the brown skin of the bulb in turpentine till it is quite 

 clear, and then mounting in balsam. In Switzerland, oxalate of potash is 



FIG. 90. WILD THYME (Thymus serpyllwn). 



IE. Step. 



A familiar wild plant with trailing stems, neat small leaves, and pale purple flowers. Like Marjoram a Labiate, and 

 aromatic. Slightly reduced. EUBOPE and N. ASIA. 



prepared from the leaves of the Common Sorrel (Rumex acetosa] and Wood 

 Sorrel (Oxalis acetosella), so plentiful are the crystals in their tissues. 



The cell-walls of the epidermis of some plants of the great Nettle order 

 (Urticacece) and a few others increase in thickness in a very peculiar manner, 

 the deposit taking the form of bladder-like growths containing carbonate of 

 lime. The cells of the Indiarubber-plant (Ficus elastica] and Common 

 Walnut-tree (Juglans regia) show these remarkable ingrowths very distinctly 

 (figs. 82 and 83). They have been christened cystoliths by the learned, a 

 name derived from the Greek kustis, a bag or bladder, and lithos, a stone. 

 Minute punctiform cystoliths, which reflect the light, are the cause of the 



