CHAP, vi The Metabolic Processes 377 



chymatous cortex, but he based his opinion upon the fact 

 that it possesses an acid reaction. He further held that 

 protein as such probably travels by the sieve-tubes, 

 which he thought to be often the places of its production. 

 His views on these points, however, were largely specula- 

 tive and based on very incomplete observations. 



Nothing further transpired till 1883, when Haberlandt 

 suggested that the laticiferous tubes are concerned in trans- 

 port, a view that met with the acquiescence of Schimper in 

 1885 and of Gaucher in 1900. Some observations made by 

 Schimper in 1885 were the first to give definite results. He 

 found that after he had removed the fibre-vascular bundle 

 of the petiole of Plantago it continued to transport its starch 

 as usual from the leaf-blade. Hence he concluded that the 

 elongated cells of the bundle-sheath form the path for sugar. 

 Von Mohl in 1885, Lecomte in 1889, and Strasburger in 

 1891, claimed that all plastic substances travel by way of 

 the phloem. Czapek in 1897 argued in favour of the path 

 being both phloem and bundle-sheath. The theory that 

 the sieve-tubes are the main channel is borne out by 

 Kraus' analysis of the contents of the sieve-tubes of 

 Cucurbita made in 1894. He found that 48 per cent, of 

 their dry weight consisted of carbohydrates. 



From some observations of Fischer in 1890, which were 

 confirmed by himself and by Strasburger in 1891, it appears 

 that besides the downward stream of organic substance 

 elaborated in the leaves there is in the spring, propelled 

 probably by root-pressure, an upward stream of organic 

 substance derived frc m the reserves stored all through the 

 winter in the roots and other perennating parts of the 

 plant. This stream supplies the young leaf-buds as they 

 resume their growth ; its path seems to be exclusively in 

 the wood. When we consider the great amount of activity 

 of the metabolic processes which follows the winter rest 

 of vegetation it becomes evident at once that the re- 



