THE MOLECULAR FORCES IN PLANTS. 227 



tion does not, as was supposed, take place in the lignified mem- 

 branes of the elements of the xylem, but in their cavities. 4 



I made investigations on this subject as follows: Two shoots 

 of Salix fragilis (a and 6) are cut and placed with their bases in 

 glasses of water. The water for a was covered with a layer of 

 olive oil : a and b were now placed in the apparatus depicted in 

 Fig. 84, the porcelain dish and crystallising glass having previ- 

 ously been supplied with Calcium chloride, and the air in the zinc 

 cylinder having been heated to 32 C. After an hour b was taken 

 out and put in a glass containing 3 per cent, gelatine solution, 

 which was then covered with olive oil. a and b were now kept in 

 the apparatus for another hour. The shoots transpired, and b in 

 doing so absorbed the gelatine solution. At the end of the time 

 both of them were taken out of the apparatus. A piece a few cm. 

 in length was cut from the base of 6, and the shoot was dipped 

 with the fresh-cut surface in water; both were now left at 20 C. 

 The gelatine stiffened in the vessels of 6, and this interfered with 

 the movement of water in them. Thus at the end of twenty-four 

 hours the leaves of b were withered, while those of the control 

 shoot a still appeared fresh. 



The following experiment leads to the same result. 5 At mid- 

 day, or in the afternoon of a sunny summer day, shoots of Vitis 

 are cut under a gelatine solution (20 parts of gelatine to 100 parts 

 of water) tinted with Indian ink. The fluid is heated to 33 C., at 

 which temperature it is perfectly fluid. If we now rapidly put 

 the shoots with their bases in cold water, and renew the cut sur- 

 face, they soon wither, since the wood elements cannot conduct 

 water owing to the plugging of their lumina by the congealed 

 gelatine. Shoots of Vitis, cut off under water and left standing 

 in it, keep fresh for a long time. (See also Strasburger's cited 

 work, p. 697.) 



As regards the forces by which the raising of water in the plant 

 is brought about, these are not yet determined with certainty. 

 Unfortunately there is still no theory as to the movement of water 

 in plants which is satisfactory from all sides. 6 Perhaps the views 

 advanced by Westermeyer and Grodlewski as to the causes of the 

 water current come nearest to the truth ; Strasburger's view, 

 however, may perhaps be correct.* We must trust to the future 



I have not yet bean able to repeat Strasburger's remarkable experiments 

 with killed plants. 



