THE MOLECULAR FORCES IN PLANTS. 235 



the rate of water conduction have gained importance, because 

 Strasburger 2 has shown that in particular eosin solutions of the 

 concentration already specified serve very well for the experi- 

 ments even with separated plant structures. The results obtained 

 with this pigment are, it is true, not absolutely exact, but still they 

 merit attention. On a hot summer day, a shoot of a plant of 

 Humulus or Bryonia growing in the open is cut through at the base 

 under water. The cut surface is now left for half an hour or an 

 hour in the water, and the shoot is then conveyed to the eosin solu- 

 tion. This precaution is necessary to prevent the pigment solution 

 being forced into the object by the atmospheric pressure. The 

 eosin rises very rapidly in the transpiring shoot. It may, e.g., 

 advance 2-3 m. in half an hour, as is shown by examination of 

 transverse sections. 



1 Sachs, Arbeiten des botan. Instituts in Wiirzburg, Bd. 2, p. 148. 



2 See Strasburger, Histologische Beitraye, Heft III., pp. 550 and 590. 



87. The Withering of Plants. 



When a plant constantly loses by transpiration more water than 

 it gains by absorption, it gradually withers. Its leaves hang 

 down limp, and if water is not supplied to it, it ultimately dries 

 up. If, however, we water the soil in flower-pots in which just 

 withered plants (e.g. beans or vegetable marrows) are growing, 

 the cells of the leaves quickly become turgescent again, and the 

 plants rapidly assume once more a fresh appearance. The same 

 thing is seen if instead of supplying water to the plants we reduce 

 their transpiration, e.g. by placing them under a bell-glass. 



If very leafy shoots of trees or shrubs are cut off and placed 

 with the lower end of their woody stems in water, they usually 

 remain fresh for days. It is therefore surprising that in some 

 plants the shoots, when so treated, wither very rapidly, in spite of 

 the fact that their steins are very woody. According to my 

 observations branches of Salix fragilis often behave in this 

 manner. In general, however, shoots cut off and placed in water, 

 remain fresh for a longer time the further the development of 

 the wood in the stem has advanced. If we cut off, for example, 

 shoots of Heliauthus tuberosus, about 1 metre in length, and 

 place them in water, they keep fresh throughout for several days ; 

 shoots 20-30 cm. long, on the other hand, very quickly wither 



