ACRIDITY OF TARO LEAVES. 69 



leaves, with deep basal sinus, and in its prickly stem. (PI. XLTX.) 

 It is very distinct, however, in having about its base the mass of 

 spines referred to. They are wiry and branching, and have very 

 much the appearance of sharp compound fishhooks. In reality they 

 are lateral roots which differ from typical monocotyledonous roots in 

 their hard woody structure and the absence of root caps. Mr. T. G. 

 Hill and Mrs. W. G. Freeman, who made a study of the root structure 

 of an allied species growing in 'Africa, found that "the lateral roots 

 form the actual spines. They only exhibit normal root-structures at 

 the extreme apex; elsewhere the phloem strands travel regularly 

 throughout the whole area of the stele, while the xylem is more or less 

 restricted to the central region. The hardness both of the main roots 

 and the spines is due to the thickening and lignification of the con- 

 junctive tissue of the stele."" Whether or not these spines have been 

 specially developed for the purpose of protecting the edible tuber may 

 be questioned, but that they do protect it is certain. 



Among the principal food staples of Guam is the taro, Caladium 

 colocasia, a plant of the Arum family. Both the land and water varie- 

 ties (PI. XXIV) are found invariably to have their smooth, succulent, 

 satiny leaves free from the ravages of snails, insects, or herbivorous 

 animals. ' Cattle and chickens delight in nipping off the young leaves 

 of bananas and plantains; deer often inflict serious injury on a young 

 coconut plantation in a single night; breadfruit trees suffer from the 

 attacks of all herbivorous animals, and must be protected from them — 

 fruit, leaves, and bark; and even tobacco will be devoured in the field 

 by insect larvae unless it is carefully watched and attended. On chew- 

 ing a small portion of a taro leaf, the cause of its safety from attack is 

 at once apparent. The tongue, roof of the mouth, and lining of the 

 throat seem to be pierced by a thousand tiny needles. The allied 

 Alocasiae, plants also belonging to the Araceae, called "piga" by the 

 natives of Guam, are so very acrid that the skin is sometimes stung 

 by merely rubbing against one of their leaves. Not only is the root 

 of the taro edible, but the tender young leaves are eaten like spinach 

 or asparagus. When not thoroughly cooked, however^ they retain 

 their acridity, and in Polj'nesia it is a common occurrence to expe- 

 rience an intense inflammation or burning of the throat after a meal of 

 savory taro tops cooked with cocoanut custard. 



Through the courtesy of Dr. H. W. Wiley, Chief of the Bureau of 

 Chemistry, United States Department of Agriculture, a careful chem- 

 ical and histological examination of fresh taro plants was made for me 

 by Mr. Lyman F. Kebler and Mr. B. J. Howard. The result of their 

 examination and experiments tends to corroborate the theory that the 

 burning sensation experienced on chewing the leaves is not caused by 

 an acrid fluid, but by minute needle-like crystals of calcium oxalate 



a Annals of Botany, vol. 17, p. 413, 1903. 



