66 CRUCIFERiE. 



verized have a greenish yellow hue. Masticated they have for an 

 instant a bitterish taste which however quickly becomes pungent. 

 When triturated with water they afford a yellowish emulsion emitting 

 a pungent acrid vapour which affects the eyes, and has a strong acid 

 reaction. The seeds powdered dry have no such pungency. When the 

 seeds are triturated with solution of potash, the pungent odour is not 

 evolved ; nor when they are boiled in water. Neither is the acridity 

 developed on triturating them with alcohol, dilute mineral acids, or 

 solution of tannin, or even with" water when they have been kept in 

 powder for a long time. 



Microscopic Structure — The whitish pellicle already mentioned, 

 which covers the seed, is made up of hexagonal tabular cells. The 

 epidermis consists of one row of densely packed brown cells, radially 

 elono:ated and having strono; lateral and inner walls. Their outer walls 

 on the other hand are thin and not coloured; they are not clearly 

 obvious when seen under oil, but swell up very considerably in pre- 

 sence of water, emitting mucilage.^ Seeds immersed in water become 

 therefore covered with a glossy envelope, levelling down the superficial 

 inequalities, so that the wet seed appears smooth. The tissue of the 

 cotyledons exhibits large drops of fatty oil and granules of albumin. 



Chemical Composition — By distilling brown mustard with water, 

 the seed having been previously macerated, the pungent prmciple, 

 Essential Oil of Mustard, is obtained. 



The oil, which has the composition SCN(C'I1®), (allyl isosulphocy- 

 anate), boils at 148° C. ; it has a sp. gr. of r0l7, no rotatory power, 

 and is soluble without coloration or turbidity in three times its weight 

 or more of cold strong sulphuric acid. To this oil is due the pungent 

 smell and taste of mustard and its inflammatory action on the skin. 

 As already pointed out, mustard oil is not present in the dry seeds, but 

 is produced only after they have been comminuted and mixed with 

 water, the temperature of which should not exceed 50° C. 



The remarkable reaction which gives lise to the formation of mustard 

 oil was explained by Will and Korner in 1863. They obtained from 

 mustard a crystallizable substance, then termed Myronate of potassium, 

 now called Sinigrin, It is to be regarded, according to the admirable 

 investigations of these chemists, as a compound of 



Isosulphocyanate of allyl or mustard oil . C* ff NS 



Bisulphate of potassium H KS O^ 



Sugar (dextroglucose) C W O' 



so 



that the formula C'" ff« KNS^ 0^ 



is that of sinigrin. It does in fact split into the above-mentioned three 

 substances when dissolved in water and brought into contact with 

 Myrosin. 



This albuminous body discovered by Bussy in 1839, but the com- 

 position of which has not been made out, likewise undergoes a certain 

 decomposition under these circumstances. Sinigrin may likewise be 

 decomposed by alkalis and, according to Ludwig and Lange, by silver 



^ Most minutely described and figured suchungen auf dem Gebiete des PJlanzen- 

 by F. von Hohnel, in Haberlandt's Unter- baties, i. (Vienna, 1875) 171—202. 



