THE SAP ASCENDS THROUGH THE WOOD. 85 



make up for the scarcity of alkaline substances in tlie soil — or would the 

 same mode of operation be emploj^ed if potash and soda were present 

 in greater abundance ? Or where the alkalies are present in greater 

 abundance, might not more work be done by them in the same 

 time, — might not the plant be built up the faster and the larger, when 

 there were more hands, so to sjjeak, to do the work ? Is the action of 

 inorganic substances upon vegetation to be explained by the existence 

 of a power resident in the roots or other parts of plants, by which such 

 operations as this are directed or superintended ? There are many 

 mysteries connected with the nature and phenomena of vegetable life, 

 which we have been unable as yet to induce nature to reveal to us.* 

 But the morning light is already kindling on the tops of the mountains, 

 and we may hope that the deepest vallies will not forever remain obscure. 



§ 3. The course of the sap. 



If the trunk of a tree be cut off above the roots, and the lower extrem- 

 ity be immediately plunged into a solution of madder or other colouring 

 substances, the coloured liquid will ascend and will gradually tinge the 

 wood. This ascent will continue till the colour can also be observed 

 in the nerves of the leaf. If at this stage in the experiment the trunk 

 be cut across at various heights, the wood alone will appear coloured, 

 the bark remaining entirely untinged. But if the process be allowed 

 still to continue when the coloured matter has reached the leaf, and after 

 some further time the stem be cut across, the bark also will appear dyed, 

 and the tinge will be perceptible further and further from the leaf the 

 longer the experiment is carried on, till at length both bark and wood 

 will be coloured to the very bottom of the stem. 



Or if the root of a living plant, as in the experiment of Macaire de- 

 tailed in a preceding note, be immersed in a metallic solution — such 

 as a solution of acetate of lead, — which it is capable of absorbing with- 

 out immediate injury, and different portions of the jjlant be examined 

 after the lapse of different periods of time,— first the stem, afterwards 

 the leaves, then the bark of the upper part of the stem, aiid lastly that 

 of the lower part of the stem, will exhibit traces of lead. 



These experiments show that the sap which enters by the roots as- 

 cends through the vessels of the wood, diffuses itself over the surface 

 of leaves, and then descends by the bark to the extremities of the root. 



But what becomes of the sap when it reaches the root? Is it deliver- 

 ed into the soil, or does it recommence the same course, and again, re- 

 peatedly perhaps, circulate through the stem, leaves, and bark ? This 

 question has been partly answered by what has been stated in the pre- 

 ceding section. When the sap reaches the extremity of the root, it ap- 

 ])ears to give off to the soil both solid and fluid substances of a kind and 



* The roots ofUrees will travel to comparatively great distances, and in various directions, 

 in search of water: the roots of sainfoin (Esjjarsette) will penetrate 10 or 12 feet thronghfhe 

 calcareous rubbly subsoil, or down the fissures of limestone rocks on which they delight to 

 grow. Is this llie result of some perceptive power in the plant — or is it merely by accident 

 that the roots display these tendencies'? 



Those who are in any degree acquainted with the speculations of the German pliysiolo- 

 gists of the greatest name — in regard to the soul and even the immortality of plants — will not 

 accuse me of going very far in alluding to the possible existence of some such perceptive 

 power in plants. Von Martins gets rid of objectors by speaking of them as " scieut^Ac men 

 to whom the power of comprehending the trenscer-dentc' has ts^.n imparled in a lower iltf «' " 

 See Meyen'sJaliresbericht, 1839, or iiilliman's Journal fcr January, 1841, p. l??. 



