1845.] Linnean Society. 229 



Read the commencement of a paper " On the Nervures of the 

 Wings in Lepidopterous Insects ; and on the genus Argynnis of the 

 ' Encyclopedie Alethodique.' " By Edward Doubleday, Esq., F.L.S. 

 &c. &c. 



Read also " Observations on the immediate causes of the Ascent 

 of the Sap in Spring." By Arthur Henfrey, Esq., F.L.S. &c. &c. 



Mr. Henfrey thinks that none of the causes generally stated, viz. 

 1. Endosmosis ; 2. Capillary Attraction ; and 3. Evaporation, are suf- 

 ficient to determine the first start of the sap. He objects to attri- 

 buting to the two first-named causes (endosmosis and cajjillary at- 

 traction) a primary part in the production of this phccnomenon, that 

 they cannot act where there is no outlet above, and where conse- 

 quently no current can take place. As regards evaporation, he is 

 inclined to believe that it does not come into operation until a cer- 

 tain quantity of the sap has been absorbed and assimilated to the 

 new tissues. He refers to the precaution taken in the autumn to 

 cover up those portions of the plant which are ex2)osed to the atmo- 

 sphere so as to protect them from its action, and to the fact that 

 buds burst forth, not from evaporation, but on the contrary, from 

 being gorged with moisture, as proofs that evaporation cannot be re- 

 garded as giving the primary impulse to the current of the sap. The 

 true cause of the ascent of the sap must, he thinks, be looked for in 

 the chemical changes which take place in the materials stored up in 

 the cells during the autumn. The insoluble grains of starch are con- 

 verted into soluble substances (dextrine and sugar) which are dis- 

 solved by the water always present in the tissues. A current is thus 

 produced by two concurrent circumstances, viz. the exhaust arising 

 from the syrup occupying less space than the materials from which 

 it was derived, and the endosmosis resulting from the increased den- 

 sity of the fluid contents of the cells. This chemical change Mr. 

 Henfrey believes to be brought about by the increase of temperature, 

 but whether it is immediately efi'ected through the action of diastase 

 or other substances he is not at present prepared to give an 

 ojtinion. 



No. XXIV. — Proceedixgs of the Linxeax SociExy. 



