[ 438 ] 



afcertain by particular attention and enquiry; as many of 

 thefe trials were made on my own children. I conclude, 

 however, that although the fame efFefls were produced, the 

 foreisjn vegetable feems to be rather more a£live than the 

 Englifli rheum palmatum, in perhaps the proportion of 

 one -third at the utmoft. 



To futn up my opinion: I conclude, that the exotic 

 plant poffefTes no one quality which the other does not 

 contain; that they are the fame produ£lion; and that, 

 probably, the fuperior activity of the former may depend 

 on circum fences of foil, time of talcing up the roots, their 

 age, and tlie methods of drying, which future enquiries may 

 doubtlefs determine. 



From fome obfervations that have occurred to me, I fuf- 

 peft tliat young plants have more mucilage, and lefs of an 

 adtive refin, than old ones ; but at what particular period 

 to fix the properefi: age for medicinal ufe, my obfervations 

 do not wairant me to decide. 



With regard to the two fpecimens of the Englifh rheum 

 palmatum marked No. I. and II. I find it difficult to give 

 the preference. I rather prefer, however, that marked No. I, 



J. C. LETTSOM, 



London, Ot7. 29, '1784. 



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LETTER 



