LIFE OF PLANTS. 24? 



V. Maurum, Diss, qua disquiritur, quousque motiis lluidonim ci cetera: 

 quaedam animalium i)lantarumque functiones consentiant. 

 Medicus in Act. Theodoro-palat. 

 Calp. Fr. Wolf, Theoria Generationi«. 

 Patr. Blair, Botanical Essays. 

 Seb. Vaillant, Discours sur la Structure des Fleurs. 

 Lefebure, Experiences sur la Germination des Plantes. 

 C. Richard. Analyse du Fruit, considere en general. 

 I- C. Treviranus, Von der Entwickelung des Embryo. 



376. 



We find other proofs of the higher Hfe of plants in the as- 

 cent of the sap, and in the distribution of it through all the 

 organs. 



It is impossible to overlook the fact, that the sap-vessels, 

 on account of Jie similarity of their structure to that of hair- 

 tubes, are chiefly appropriated to the purpose of raising the 

 sap to a certain height, (276.) But were the sap-vcsscls 

 simply hair-tubes, it were impossible to explain why the sap 

 in them rises constantly to a greater height, since the hair- 

 tube retains the fluid which it has once taken up, at one fixed 

 height. It would also be impossible to explain why light 

 has so powerful an influence upon the ascent of the sap, since 

 fluids, in hair-tubes, stand as high in the dark as in the light 

 of the sun. 



Neither heat, nor the pretended hygroscopical nature of the 

 vessels of plants, can altogether explain this phenomenon ; be- 

 cause, were the ascending sap attenuated by heat, and were 

 the upper parts of the sap- vessels rendered, by the same 

 means, more fitted for receiving the attenuated sap, the heat 

 of the upper aerial strata must always be greater thiui tliat of 

 the earth around the roots. But in hot-beds, and in hot- 

 houses, we only bring plants to a lively growth, when we ren- 

 der the earth about the roots much Avarmer than the strata of 

 air above the earth ; and it is not possible, therefore, to ex- 

 plain the ascent of the sap from this attenuation by heat. The 

 hygroscopic nature of the vessels of plants is scarcely worthy 

 of a refutation, since the moisture, which constantly sur- 

 rounds them on all sides, directly contradicts this explana- 

 tion. 



