CHAPTER V 



CELL-CONTENTS (BY-PRODUCTS, ETC.) 



THE by-products comprise chemical compounds formed during 

 the metabolism of the plant which do not, as far as our present 

 knowledge goes, appear to play any further part in the elabora- 

 tion of food-substances. This does not, however, mean that 

 they fulfil no functions in the living organism, for they may be 

 of importance in warding off the attacks of preying animals, in 

 the creation of attractive mechanisms, in the reduction of trans- 

 piration, etc. 



One of the most widespread of the by-products is oxalate 

 of lime, which may occur in practically every organ and tissue 

 of the plant. It is produced by the neutralisation of the oxalic 

 acid formed during metabolism and, being insoluble, appears in 

 the shape of crystals which assume diverse forms. Large 

 solitary crystals (Fig. 25, C), each occupying the greater part of 

 the cell-contents, are very common; but most frequent are 

 clusters, or rosettes, of crystals radiating from a dark centre 

 (Fig. 25 , A) . Another widespread type takes the form of bundles 

 of needle-shaped crystals (raphides) , generally situated in enlarged 

 cells containing mucilage (Fig. 25, B). This last type is particu- 

 larly characteristic of the Monocotyledons, though by no means 

 lacking in Dicotyledons (e.g. Enchanter's Nightshade) . In some 

 few cases, especially in the Solanacese, the oxalate of lime is 

 deposited in the form of a powder-like mass of numerous very 

 minute crystals (so-called crystal-sand). 



Crystals of calcium oxalate are always found in quantity 

 where active metabolism is going on. They are often very 

 abundant in the tissues adjoining actively secreting organs 



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