THE CONDUCTION OF WATER. II 



75 



According to R. H artig ( 1883, p. 73) the spruce stem becomes incapable of convey- 

 ing water when the lumina of the tracheids are still more than half full of water. 

 Apart from this, however, living tissues, especially the parenchymatous cells, 

 which are almost always associated with the vessels, may take part in water 

 conduction directly or indirectly. Westermaier (1884), Godlewski (1884), and 

 Janse (1887) have assumed that the parenchyma play a direct part in the process. 

 The essential point in all these theories is that parenchymatous cells abstract 

 water from one vessel and hand it on to one higher up. A complete discussion 

 and criticism of these views (Zimmermann, 1885, Schwendener, 1886) need not 

 be presented here, since, owing to the researches of Strasburger, all such 

 vital theories have received a severe blow, if indeed they have not been directly 

 disproved. Further, no positive evidence has been advanced in support of these 

 theories, and one accepted them because purely physical explanations appeared 

 to be inadequate. 



Experiments on the ascent of sap in dead branches had been previously 

 carried out, but for the most part these were confined to killing short lengths 

 and establishing the fact that they were permeable to water. Naturally, it 

 cannot be concluded from such experiments whether, in stems of any length, 

 water conduction goes on after the death of the parenchyma. Such researches 

 on a large scale we owe to Strasburger (1891, 1893). He killed long 

 branches of Glycine, by placing the lower leafless part, which was 10-12 m. 

 in length, in boiling water, and observed that an eosin solution rose in them from 

 the cut end to a height of i6-8 m. ; still the leaves which were present at the un- 

 injured end of the stem remained alive for only a few days, after which they dried 

 up and fell off. In all probability the deficiency in the supply of water to the apex 

 was not due to the death of the parenchyma but to the fact that masses of slime 

 and other obstructions entered the vessels, in the way we have already described. 



Strasburger has also killed long reaches of plant stem otherwise, 

 e. g. by poisons, and proved that they are still capable of conducting water 

 in the dead condition. The following extract may be selected from the de- 

 scription of one of his numerous experiments (Strasburger, 1893, p. 10). 



' The summer oak selected for experiment was 21 7 m. high, 27 cm. thick, at 

 a height of 10 cm. above ground, and 75 years old. On June 28, about 4 p.m., 

 the tree was sawn off, obliquely, 10 cm. above ground, while water flowed 

 rapidly in the cut. The severed trunk was at once raised to a vertical position 

 and suspended in a tub of water. It remained in this tub about half an hour, 

 whilst its cut surface was cleaned and smoothed with a sharp knife. The tree 

 was then put into a vessel filled with a saturated solution of picric acid, which 

 is intensely poisonous to the plant. It was sunk about 20 cm. in this fluid.' 

 The upper limit of the solution in the vessel was noted and the amount kept 

 constant by filling the vessel up to this level morning and evening each day. 



The amounts of fluid absorbed by the stem were as follows : — 



Hours . 

 Litres . 



IX. 

 D. N. 



12 

 0-3 



12 

 I 



It is clearly seen that considerably greater amounts of water were taken 

 up at first during the day than during the night, although the period of observa- 

 tion termed ' night ' for short was markedly longer than the 'day'. Later, 

 after the leaves had died, this periodicity ceased and the absorption of fluid 

 as a whole fell ofl very considerably. After the fourth day the picric acid had 

 risen up the stem to a height of 15 m. and had killed these parts ; when fuchsin 

 was added to the solution the rise of this colouring matter could be followed 

 in the dead stem. At the end of the experiment, on the tenth day, it was 



