ON GROWTH AND EXTENSION IN THE VEGETABLE KINGDOM. ^1 1 



the top, yet the branch continues to grow. In this case it is 

 clear that the sap must pass laterally into other vessels or cells, 

 in order to resume its right direction upwards. 



That the sap rises in tlie vessels, not in the cellular tissue, I 

 endeavoured to prove by experiments which I related in the 

 Annales des Sciences Naturelles, vol. 23, p. 144. I took Rhagodia 

 Billardieri, Begonia divaricata, Stylidium fruticosum, and Her- 

 mannia altlieaefolia, and placed each of these plants, with the pots 

 in which they g'rew, into a trough filled with a solution of red 

 prussiate of potash in 32 parts of water. For eight days they were 

 fed with this solution, in which they appeared to thrive ; I then 

 removed the trough, and replaced it hj another filled with a 

 solution of sulphate of iron in 32 parts water. After twenty-four 

 hours I examined the plants and found the vessels, the spiral as 

 well as the porous vessels, filled with a blue liquid. I admit 

 tliat these experiments do not always succeed ; many accidents 

 prevent the prussiate of potash from being taken up by the vessels, 

 or from remaining in them ; but all tlie experiments agreed in 

 showing: that these solutions did not rise throuoh the cellular 

 tissue of the bark, the wood, or the pith. The experinient can 

 be varied in many ways. I watered some tulips growing' in a 

 pot with a weak solution of prussiate of potash — for if the roots 

 themselves are immersed in the solutiDU they will not bear it 

 long — then I cut otf the stem, and immersed it in a solution of 

 sulphate of iron, upon which the vessels alone appeared blue on 

 examination, the adjoining cells not in the least so. 



linger has, however, latterly endeavoured to show that the sap 

 really rises in the cellular tissue which surrounds the vessels.* 

 He watered some white-flowered hyacinths growing in a pot with 

 the juice of Phytolacca decandra, and saw that the flowers, the 

 upper part of the stem, and the upper portion of the leaves 

 became tinged with red. A microscopical examination showed 

 that tlie spiral vessels were not at all coloured, but tliat the sur- 

 rounding cellular tissue was coloured red. Unger adds, " The 

 comparison of all the organs showed that the lower ones, the 

 fibrous roots, remained quite free of all colouring matter ; the 

 base of the bulb, the lower part of the stem and of the leaves, as 

 well as the scales of the bulb, had a small portion of the colouring 

 matter, and that it was the outer extremities of the flowers and 

 the points of the leaves that held the greatest mass of it, and were 

 consequently the most intensely coloured." In this there is some 

 vagueness. What is the meaning of a smaller portion of colour- 

 ing matter ? Were the cells themselves of a paler colour, or was 



* On the Absorption of Coloured Matters by Plants, by Dr. F. Unger. 

 Vienna, 1849. 



