SEMEN RICINI. 569 



large tuiniJ caruncle: from this latter proceeds the raphe as far as the 

 lower end of the ventral surface, where it forks, its point of disappear- 

 ance through the testa being marked by a minute protuberance. If the 

 caruncle is broken off, a black scar, formed of two little depressions, 

 remains. 



The shining grey epidermis is beautifully marked with brownish 

 bands and spots, and in this respect exhibits a great variety of colours 

 and markings. It cannot be rubbed off, but may after maceration be 

 peeled off in leathery strips. The black testa, grey within, is not 

 thicker than in croton seed, but is much more brittle. The kernel or 

 nucleus fills the testa completely, and is easily separated, still covered 

 by the soft white inner membrane. 



The kernel in respect to structure and situation of the embr^^o, agi'ees 

 exactly with that of Croton Tiglium (p. 565), excepting that the some- 

 what gaping cotyledons of Ricinus are proportionately broader, and have 

 their thick midrib provided with 2 or 3 pairs of lateral veins. If not 

 rancid, the kernel has a bland taste, with but very slight acridity. 



Microscopic Structure — The thin epidermis consists of pentagonal 

 or hexagonal porous tabular cells, the walls of which are penetrated in 

 certain spots by brownish colouring matter, whence the singular 

 markings on the seed. It is these cells only that become blackened 

 when a thin tangential slice is saturated with a solution of ferric chloride 

 in alcohol. 



Beneath these tabular cells there is found in the unripe seed^ a row 

 of encrusted colourless cells, deposited in a radial direction on the testa. 

 In the mature seed this layer of cells is not perceptible, and therefore 

 appears to perish as the seed ripens. The testa itself is built up of 

 cylindrical, densely packed cells, 300 to 320 mkm. long, and 6 to 10 

 mkm. in diameter. The kernel shares the structure of that of C. Tigliwm, 

 but is devoid of crystals of oxalate of calcium. If the endopleura 

 of Riciiius is moistened with dilute sulphuric acid, acicular crystals of 

 sulphate of calcium separate from it after a few hours. 



When thin slices of the kernel are examined under concentrated 

 glycerin, no drops of oil are visible, notwithstanding the abundance of 

 this latter; and it becomes conspicuous only by addition of much water. 

 Hence it is probable that the oil exists in the seed as a kind of 

 compound with its albuminoid contents." As to the latter, they partly 

 form in the albumen of Ricinus beautiful octohedra or tetrahedra, 

 which are also found in many other seeds. ^ 



Chemical Composition — The most important constituent of the 

 Iseed is the fixed oil, called Castor Oil, of which the peeled kernels 

 afford at most half of their weight. 



The oil, if most carefully prepared from peeled and winnowed seeds 

 by pressure without heat, has but a slightly acrid taste, and contains 

 only a very small proportion of the still unknown drastic constituent of 

 the seeds. Hence the seeds themselves, or an emulsion prepared with 



* Gris, Annales des Sciences I<^at., Bot., Krystalle jyroteinartiger K&i-per, Leipziff, 



XV. (1861) 5-9. 1859. 61. and tab. 2 fig. 10; Pfeffer, Pro- 



- Sachs, Lehrhiich der Botan'd; 1874. 54. telnkorner in Pringsheim's Jahrbiicher fitr 



^ For further particulars, see Ti-ecul, .4 ;in. wissenschaftliche Botanik, viii. (1872) 429. 



deaSc. JVa<., Bot.,x., (1858) 355 ; Radlkofer, 464. 



