18 EXPERIMENTAL PLANT PHYSIOLOGY 



of this phenomenon has yet been advanced. The 

 mighty force great enough to raise water to the top- 

 most branches of the tallest trees, against the opposing 

 force of gravity, is still a mystery. 



By means of red ink or other coloured solutions it 

 has been demonstrated that the water taken in by the 

 root passes up through the stem and reaches the 

 leaves. But although the leaves have become red the 

 colour of the stem externally is unaltered. The ink 

 caimot, therefore, have passed through the bark; it 

 must have gone up through the inner part of the stem. 



Experiment 8 



Aim. — To find out where the water passes up the 

 stem. 



Method. — Three leafy twigs should be used, two 

 being those of dicotyledons having respectively a 



b; moMTOt'ylTdonous stem. \ '•''■''"=™"« »i?.'l longitudinal 



0, herbaceous stem. / sections. 



y, pith, w, wood. 6 +c, bast and cortex. M, bark. 



mr, medullary ray. g, ground tissue. 



The distribution of the tissue which stains red is shown in each ease. 



Fig. 6 



woody stem {e.g. beech, hme) and a herbaceous stem 

 {e.g. sunflower, hogweed), and the third that of a 



