158 



SEEDS 



is black and bears a distinct brown furrow in its centre. This deep 

 groove is the hilum, and in it may frequently be found portions of a 

 white, papery funiculus ; at one end a minute depression (the micropyle) 

 can be detected. 



The outer seed-coat (testa) is hard and thick, and appears nearly 

 smooth to the naked eye, but under the lens is seen to be rather rough. 

 After the seeds have been well soaked in water they can easily be split 

 longitudinally, and exhibit then two firm white starchy cotyledons, 

 which are curved so as to include between them a large lenticular cavity 

 filled with air ; this enables the seed to float when thrown on the 

 surface of water. Near the micropyle is the small white radicle attached 

 to one of the cotyledons ; there is no endosperm. 



The seeds have no marked odour or taste beyond 



those of an ordinary bean ; they are nevertheless 



extremely poisonous. 



The student should observe 



(a) The reniform (not cylindrical) shape, and 



the hilum passing round one end of the 

 seed, 



(b) The white cotyledons and small radicle 



directed towards the micropyle. 



Constituents. The principal constituent of the 

 Calabar bean is the alkaloid physostigmine (also 

 called eserine, from ' esere,' the native name of the 

 bean) ; it is present in the cotyledons only and to 

 the extent of about 0-2 (0-04 to 0-3) per cent. The 

 bean also contains the alkaloids eseramine (trace 

 only), physovenine (Salway), and geneserine (Polo- 

 nowski, 1915) ; stigmasterol, sitosterol, and the 



dihydric alcohols trifolianol and calabarol, and abundance of starch. 



The drug yields about 4 per cent, of ash. 



Physostigmine, C 1B H 21 N3O 2 ,- forms colourless rhombic crystals melting at 

 105 ; aqueous solutions of its salts rapidly become pink, due to conversion 

 of the physostigmine into rubreserine ; it powerfully contracts the pupil of 

 the eye. 



Physovenine, C 14 H 18 3 N 2 , has been obtained in colourless crystals, strongly 

 mydriatic ; traces only. 



Eseramine crystallises in needles melting at 238. 



Geneserine yields a crystalline salicylate; the physiological action differs 

 from that of physovenine. 



Calabarine and eseridine, formerly considered constituents of the seed are 

 now regarded as non-existent. 



Substitutes. P. cylindrospermum, Holmes ; seed nearly cylindrical, 

 hilum shorter ; were imported in 1879 and are said to contain 

 physostigmine. 



FIG. 89. S e e d 

 of Physostigma 

 cylindrospermum, 

 showing the 

 shorter hilum. 

 (Maisch.) 



