70 USEFUL PLANTS OF QUAM. 
(Pl. XJ) contained in their tissue, Many plants in which these erys- 
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. (Pl. XII.) When the vacuoles become filled 
with water by 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 
amelie by what appeared to be a series of explosions. In Pl. 
XI, tig. 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,’ 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 _ capsule recoiled 
like a gun which has been fired. In Pl. 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 empty 
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. Suflicient heat is not always 
developed in boiling to effect the change. Pl. 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: 
[ 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. Nut. 2° serie, vol. 6, p. 18, 1836, 
