BY JAMBS M. PETRIB. 



537 



For comparison with the preceding, the amount of acid present 

 in the common nettle (Urtica urens) was determined, under 

 precisely similar conditions. 



100 grams of fresh young nettle leaves were distilled with 

 phosphoric acid into standard alkali, and on titration gave an 

 amount equivalent to 0002 % of formic acid. 



Another 100 grams were dried at 120° C. and then distilled as 

 before. The distillate contained no trace of a volatile acid, 

 showing that the latter had been completely volatilised in drying. 



The whole of the acid in the common nettle is therefore free 

 uncombined formic acid, and the amount in the specimen tried 

 was 0-002%. 



Microscopic Structure op the Hairs. 



The whole of the surface of the leaves and stalks is covered 

 with an infinite number of minute hollow hairs. More sparsely 



$SS* 



Fig. 1. — Stinging hairs of Laportea gigas. 

 distributed among these are certain very large hairs, which are 

 strong and rigid, and each one is fixed by a bulbous root in a 

 raised mound or basal cushion. The latter is green and cellular, 

 and is likewise covered with the minute hairs. 

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