PHYSOSTIGMA. CALABAR BEAN. 243 



nearly the entire length of the curved side, and passing 

 completely around one end of the seed, runs a broad, deep 

 groove, the lips of which are thickened and paler in 

 color and the bottom of which is black and bears a dis- 

 tinct brown furrow in the centre. In this hilum there 

 are frequently portions of a white papery funiculus. At 

 one end the micropyle can be detected as a minute de- 

 pression. 



Histology. — On cross-section near the chalaza four dis- 

 tinct tissues can be made out. 



The external layer consists of closely appressed cylindri- 

 cal cells with small lumen. These are one layer thick 

 and have a palisade arrangement. Externally the ends 

 are square, internally rounded and passing into the 

 second row of tangential ly arranged cells. These are 

 more irregular and have thick walls and brownish cell 

 contents. A number of air spaces are found in this layer. 

 The third layer consists of much more irregularly ar- 

 ranged cells. The last layer consists of flattened, dark- 

 brown, tangentially arranged, thin-walled cells, under 

 which the parenchyma of the cotyledons is found. This 

 is made up of large cells, the outer layers being smaller 

 and more regularly arranged. The cells contain large 

 amounts of starch and a number of protein granules. The 

 starch is ample and consists of large, elliptical grains 

 with irregular hilum, and by polarized light shows curved 

 lines similar to those found in papilionaceous starches. 



Chemistry. — Taste and smell are similar to those of 

 other members of the bean family. Starch, 40 to 50 per 

 cent.; proteids, 23 per cent.; 3 per cent, ash; mucilage. 

 The most important constituent is the alkaloid phy- 

 sostigmine (eserine). Hesse proposed the formula 



Hamack and Witowski have isolated a second alkaloid, 

 which they have called calabarine. This, they state, is 

 allied to strychnine. The alkaloids are found in the 



