MECHANICAL EFFECT OF OSMOSE ON PLANTS. 407 



v^ 



mant, shortly exhibit signs of growth, 

 and if the cut end be immersed in wa- 

 ter, the buds will enlarge quite after 

 the normal manner, as long as the nu- 

 trient matters of the twig last, or until 

 the tissues at the cut begin to decay. 

 It is the summer temperature which 

 excites the chemical changes that re- 

 sult in growth. Water is needful to 

 occupy the expanding and new-form- 

 ing cells, and to be the vehicle for the 

 translocation of nutrient matters from 

 the wood to the buds. Water enters 

 the cut stem by imbibition or capillar- 

 ity, not merely enough to replsice loss 

 by exhalation, but is also sucked in by 

 osmose acting in the growing cells. 

 Under the same conditions as to tem- 

 perature, the twigs which are connected 

 with active roots expand earlier and 

 more rapidly than cuttings. Artificial 

 pressure on the water which is pre- 

 sented to the latter acts with an effect 

 similar to that which the natural stress 

 caused by the root-power exerts. This 

 fact was demonstrated by Boehm 

 {Sitzungsberichie der Wiener Akad., 

 1863), in an experiment which may be 

 made as illustrated by the cut. Fig. 70. 

 A twig with buds is secured by means 

 of a perforated cork into one end of a 

 short, wide glass tube, which is closed 

 below by another cork through which 

 passes a narrow syphon-tube, B. The 

 cut end of the twig is immersed in 

 water, W, whicli is piit under pressure 

 by pouring mercury into the upper 



