1902] RISE OF THE TRANSPIRATION STREAM 169 



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osmotic strength with any approach to exactness, but they still 

 indicate that it is far more than sufficient to account for the 

 accompanying pressure. On the other side is a statement by 

 Duchartre (1859) that the water guttated by Colocasia is almost 

 like distilled. The analysis was by Berthelot, who found traces 

 of KCl, CaCOg, and organic matter. The earlier statement by 

 Schmidt, who does not seem to have evaporated the water, that 

 the guttated fluid is chemically pure water, is discordant with 

 all modern results. Unger ( 1S58) found 0.056 per cent, of solid 

 matter in it. For other literature see Burgerstein (1889:405). 

 To account osmoticallv for this oruttation the water would have 

 to be more concentrated than that absorbed by the roots by 

 perhaps 0.03 per cent, of KCl. 



According to Strasburger ( 1891 :85i), *' Belegzellen "are rich 

 in content during the time of bleeding, but not afterward. Still, 

 Strasburger doubts their passing this content into the tracheae, 

 and so setting up a root pressure; but his reason against this 

 seems to be chiefly a priori, and based on the unsound assump- 

 tion that the cells would be obliged to lose the sap in the same 

 concentration in which they hold it. 



In herbs, especially in young seedlings, it is very common to 

 find bleeding or guttation during only a part of each day. The 

 same plants in which guttated drops are found in the morning 

 are likely to contain air under a decidedly diminished pressure 

 in the afternoon. The reason is that the roots cannot furnish 

 water as rapidly as it evaporates. But it is also possible that the 

 activijty of the roots is less by day, the removal of the hydro- 

 static pressure in the tracheae stimulating the active cells to 

 become less permeable to their solutes' on that side, and so 

 economize their contents when it would be useless to let it 

 escape. Labillardiere, according to various text-books, says the 

 palm Arenga saccharifera bleeds a sap richer in sugar by night 

 than by day. The daily periodicity in pressure occurs also in 

 trees. The bleeding of Carpinus (Strasburger, 1891:841) 

 begins during the nis^ht and ceases before noon. Birches may 



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also cease to bleed before noon (Detmer, 1887), but may con- 



