70 USEFUL PLANTS OF GUAM. 



(PI. XI) contained in their tissue. Many plants in which these crys- 

 tals are found are not acrid to the taste, but most of the Araceae, 

 including- our own Indian turnip, or jack-in-the-pulpit, are intensely 

 so. In some plants the crystals are developed singly in a cell of the 

 parenchyma; in other cases they are in the form of a radiating clus- 

 ter, while in others, including several families of monocotyledons, 

 they form compact bundles, called raphides. These raphides are some- 

 times found in a cell which can not be easily separated from the 

 remaining tissue of the plant. In the genera Caladium and Alocasia 

 they are inclosed in what appears to be an elongated transparent cap- 

 sule filled with mucilage. These capsules, or cartridges, are situated 

 in the partition wall between two vacuoles, their ends projecting into 

 the adjacent vacuoles. (PI. XII.) When the vacuoles become filled 

 with water hy being crushed in chewing or when artificially macerated, 

 the mucilage absorbs water through the capsule walls, increasing; in 

 volume so that it exerts such a pressure that the needles are ejected 

 with considerable force from the capsule at one or both ends, where 

 the cell wall is thinner than at the sides. 



While Mr. Howard was examining a section containing some of 

 these raphides, the capsules absorbed water and began to discharge 

 themselves b^y what appeared to be a series of explosions/' In PI. 

 XI, fig. 1, is shown a section of taro leaf multiplied by 100 diam- 

 eters, with the raphides in place. The thirsty mucilage, as it has been 

 called by one author, 6 has absorbed a certain quantity of water and 

 some of the needles have been forced out. In fig. 2 is shown a single 

 capsule discharging the needles at both ends, the distance to which 

 they have been projected to the right showing that the force of the 

 discharge was considerable. At every discharge the capsule recoiled 

 like a gun which has been fired. In PI. XII, fig. 1, is shown a cross 

 section of the blade of a taro leaf magnified 300 diameters. This 

 shows a capsule in place, with its ends projecting into adjacent empt} r 

 vacuoles. Fig. 2 shows a similar cell in the tissue of the petiole. 

 These capsules retain their power to absorb water and discharge 

 their needles after the leaf has been thoroughly dried. They must be 

 subjected to great heat to lose their activity; and when this is lost, as 

 in cooking, the plant is no longer acrid. Sufficient heat is not always 

 developed in boiling to effect the change. PI. XIII shows single 

 capsules, or "bombs," as Doctor Wiley has called them, in fig. 1 just 

 beginning to discharge its needles and in fig. 2 in full action. Doctor 

 Wiley in his description says: 



I immediately took Mr. Howard's place at the microscope and saw for a period of 

 five or ten minutes a most remarkable display. Continual discharges were made 

 from this bomb, the ends of the arrows spreading out as they emerged in groups of 



«See Doctor "Wiley's account in Science, July 24, 1903. 

 &Turpin, Ann. des Sci. Xat. l )l ' serie, vol. 6, p. 18, 1836. 



