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The ujisatisfactory Nature of the Theories proposed to account 

 for the Descent of the Radicles in the Germination of Seeds 

 shewn by Experiments. By Henry Johnson, Esq. Mem- 

 ber of the Royal Medical Society of Edinburgh. 



i HE singular tendencies of the plume and radicle, the one in- 

 variably upwards into the air, the other downwards into the 

 earth, which are among the most curious phenomena of vegeta- 

 tion, have been variously accounted for by several distinguished 

 phytologists. Theories have been framed by MM. Parent *, 

 Du Hamelf, and De Ja Hire J, by Dr Darwin ||, and by Mr 

 Knight §. None of these, however, excepting the two last men- 

 tioned, appear to have attracted much attention, or met with any 

 advocates among modern botanists. 



The interesting nature of this subject, and the desire of learn- 

 ing the cause of these opposite and singular tendencies, have in- 

 duced me to pay considerable attention to the phenomena, and 

 to perform many experiments, several of which, I believe, are 

 original ; and the results of which appear not easily reconcilable 

 with the theories above mentioned. In the present communica- 

 tion, therefore, I shall as shortly as possible adduce a few of 

 these ^, and the conclusions to which they seem to lead, confin- 

 ing my remarks at present principally to the cause of the de- 

 scent of the radicle. 



I. According to the theory of Dr Darwin, " the plumula is 

 stimulated by air into action, and elongates itself where it is 

 most excited ; and the radicle is stimulated by moisture, and 

 elongates itself where it is most excited.'"' — Phytolog. p. 144. 



ExpER. I. — A small slip of tinned iron, about three-fourths 

 of an inch in diameter, was bent into a circular form, and to the 



• Physique des Arbres. li Davy's Agricult. Chem. 



\ Physique dcs Arbres. g Philos. Trans. Lond. 1806. 



X Phytologia, p. 144. 

 H The experiments contained in this communication were related in a 

 paper read before the Royal Med. Soc. of Edinb. in January 1828. 



