112 PROCESS OF NUTRITION. CHAP. III. 



fancy ; and as the obscurity as well as importance 

 of the subject demanded, so it gave origin to fur- 

 ther investigations. 



It occurred to succeeding phytologists that the 

 progress of the sap, and the vessels through which 

 it passes, might be traced or ascertained by means 

 of making plants to vegetate in coloured infusions; 

 and accordingly plants were made so to vegetate. 

 The earliest experiments on the subject seem to be 

 those of Magnol, instituted about the beginning of 

 the eighteenth century, though it does not appear 

 that his object was any thing beyond that of merely 

 demonstrating the ascent of the sap to the very 

 summit of the plant. The colouring matter he 

 made use of was the juice of Phytolacca ; and 

 when the extremity of a stem of the Tuberose was 

 moistened in an infusion of this juice, it was found 

 to mount up to the summit and to give a red colour 

 De la to the flower. M. De la Baisse, improving upon 

 this hint, instituted a number of experiments, with 

 the same juice, upon a great variety of different 

 plants, and found that the infusion always left 

 behind it some evident traces of its ascent in the 

 form of longitudinal streak? or threads. In the 

 root, it was found that the smaller divisions were 

 always tinged more deeply, and the larger divisions 

 more faintly ; the tinge being also deeper as it ap- 

 proached the centre. In stems of the Peach and 

 Elm, of from three to four feet in length, the 

 coloured tubes were traced to the extremity of the 



