been named from a fancied likeness of the radiately thorned 
fruit, to the instrument called Caltrops, formerly used as a 
defence against cavalry. ‘rapa is a Linnean elision of 
Calcitrapa, which last means the same as Caltrops; so 
does Tribulus, the classic appellation of the plant. The 
fruit or nut is of a turbinate shape, one-seeded, ripens under 
water, resembles in its nature the Chestnut, and is eaten 
like that at the dessert, either roasted or boiled. The 
outermost covering, a somewhat fleshy opaque membrane, 
is readily stripped off, when the fruit, generally about an 
inch in diameter, shows itself with the same sort of shining 
brown coriaceous ¢esta or kernel-coat, which belongs to the 
Chestnut. The kernel is sometimes made into flour, which 
serves for porridge, and even for bread in several European 
countries, especially Carinthia. At Venice the fruit is sold 
by the name of the Jesuit’s Nuts. “The Germans call it the 
Water-nut. The French Macre. Children eat it raw. The 
Chinese are said to cultivate another species (bicornis) in 
their undrained water-lands, as a substitute for bread-corn. 
Rootstock of various lengths according to the depth of 
the water, furnished at the joints with distinct tufts of roots; 
each tuft consisting of an axis, surrounded by numerous 
horizontal capillary radicles, gradually shortening from bot- 
tom to top, and forming a pyramidal plume. ‘These have 
been generally looked upon as the water-leaves, but we do 
not see why. Caudex continuous, surrounded by a close 
alternately disposed pedicled foliage, displaying a bright 
green star at the surface of the water; leaves about an inch 
and half broad, rhomboidal, thickish and nerved, bimu- 
cronately toothed, subpubescent at the nerves underneath: 
etiole 2-3 times longer, distending just below the blade 
into an oblong intuimescence, something like a small angler’s 
float, filled with cellular pith, and acting as a buoy. 
Flowers small, white, submerged, pellucid: peduncles soli- 
tary, 1-flowered, axillary, enlarging as the fruit grows. 
Allioni ascribes to the flower a membranous persistent nec- 
tary, plaited in the form of a star, which no one else seems 
to have observed. The anthers part with the pollen under 
water before the calyx opens. ‘The thorns on the fruit are 
formed by the extension and induration of the 4 segments 
of the calyx. The kernel-coat never opens spontaneously, 
and the seed germinates through a small aperture at the top 
previously closed by a thin membrane and converging villi. 
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