106 SECRETION. 



and though the interior of the stem is the more 

 common situation for them, they may be found else- 

 where ; according to some they are deposited within 

 cells, and according to others in intercellular spaces ; the 

 first is regarded by Mr. Quekett as their true situation, 

 when we would express the general rule. 



134. Turpin supposed, that particular plants possess 

 a certain form of crystal, and that other plants show 

 no traces of them, and that the presence of these 

 crystals was sufficient to distinguish the Russian and 

 Chinese Rhubarbs from others. On this Mr. Perreira 

 remarks, that in some specimens of English Rhubarb 

 these crystals are in as great abundance as in foreign 

 Rhubarb ; and Meyen states, he has found them in every 

 description of Rhubarb that he has examined. 



135. According to Mr. Quekett, " Raphides appear to 

 be compounds that become crystallized merely by the 

 slow admixture of their constituents, and are probably 

 modified by gummy, amylaceous and other matters, which 

 are contained in the juices of the plant. Their forma- 

 tion does not seem confined to living structures, or 

 to any particular tissues or organs of a plant : but the 

 process may be carried on in any situation, as can be 

 proved in the Grape Vine, in which crystals can be dis- 

 covered in every organ, and in the vascular as well as 

 in the cellular tissue." 



136. Before leaving this subject we may notice a cir- 

 cumstance or two connected with the secreting powers 

 of plants. 



137. Duhamel made the observation that a peculiar 

 slimy matter showed itself at the ends of the radicles of 

 such plants as were reared in water, and proposed the 

 question as to whether it was to be considered as a 

 matter separated from the sap. Brugmans remarked 

 that the roots of various plants which had been removed 

 with great care from the earth, secreted at their extre- 

 mities little drops of a slimy nature, and which chiefly 

 took place during the night. From various experi- 



