RADIX RHEI. 491 



grains. Their colour is a light pinkish grey with an elongated brown 

 spot on the vaulted back, due to the embryo, which at this point is in 

 close contact with the translucent testa. From this brown spot the 

 thick radicle runs to the top of the seed. The hollow side of the seed 

 is also brown and partially covered with a thin white membrane. 



The seeds are highly mucilaginous in the mouth, but have neither 

 taste nor odour. Those of the allied P. Psylliiiin have nearly the same 

 form, but are shining and of a dark brown hue. 



Microscopic Structure — This can be best investigated by immers- 

 ing the seed in benzol, as in this medium the mucilage is insoluble. 

 When thus examined, the whole surface is seen to consist of polyhedral 

 cells, separated by a very thin brown layer from the albumen, which on 

 the back of the seed is only 70 mkm. thick. The albumen is made up 

 of thick-walled cells, loaded with granules of matter which acquire an 

 orange hue on addition of iodine. The two cotyledons adhere in a direc- 

 tion perpendicular to the bottom of the furrow ; their tissue is composed 

 of thin-walled smaller cells, containing also albuminous granules and 

 drops of fatty oil. 



If the seed is immersed in water, the cells composing the epidermis 

 instantly swell and elongate, and soon burst, leaving onl}^ fragments of 

 their walls. When examined under glycerin, the change is more gradual, 

 and the outer Wcills of the cells yielding the mucilage display a series of 

 thin layers, which slowly swell and disappear by the action of water. 

 The mucilage is consequently not contained within the cells, but is 

 formed of the secondary deposits on their walls, as in linseed and 

 quince pips. 



Chemical Composition — Mucilage is so abundantly yielded by 

 these seeds, that one part of them with 20 parts of water forms a thick 

 tasteless jelly. On addition of a larger quantity of water and filtering, 

 but little mucilage passes, the greater part of it adhering to the seeds. 

 The mucilage separated by straining with pressure does not redden 

 litmus, is not affected by iodine, nor precipitated by borax, alcohol or 

 ferric chloride. The fat oil and albuminous matter of the seed have 

 not been examined. 



Uses — A decoction of the seeds (1 p. to 70 p. of water) is employed 

 in India as a cooling, demulcent drink. The seeds powdered and mixed 

 with sugar, or made gelatinous with water, are sometimes given in 

 chronic diarrhoea. 



POLYGONACE^. 



RADIX RHEI. 



Rhubarb; F. Rhubarbe; G. Bhabarber. 



Botanical Origin — No competent observer, as far as we know, has 

 ever ascertained as an eye-witness the species of Rheum which affords 

 the commercial rhubarb. Rheum officinale, from which it seems, at 

 least partly, derived is the only species yielding a rootstock which 

 aofiees with the drusf. 



