9 o 



THE VEGETATIVE ORGANS 



Water, however, is absorbed and serves to keep the shoot 

 fresh, while that in eosin becomes discoloured and dies. 

 Judging from these experiments we may conclude that 

 the wood of such a shoot is the path along which water 

 ascends through the stem to the leaves. But what of the 

 other tissues of the bundle, for example the bast ? 



If we examine the plants in a garden or park, especially 

 shrubs or trees which have been tied for some time to 

 a support, it will be interesting to note 

 the mode of growth in the neighbourhood 

 of the ligature. Fig. 54 is a sketch of 

 a rose stem which has been tied in this 

 way and allowed to grow for some time 

 without further attention. Careful ex- 

 amination of such a shoot shows that, as 

 the stem has grown in thickness, the 

 ligature has gripped it with increasing 

 pressure, and the delicate tissues of the 

 inner cortex and bast have been so com- 

 pressed that substances could not pass 

 along them, but the rigid walls of the 

 woody tissues have withstood the pressure, 

 and sap can still ascend as usual. The 

 chief changes noted, however, affect the 

 portion of the stem above the ligature, 

 materials have accumulated, obviously 

 carried from a higher level, and have become stored in 

 an abnormal tissue which forms a swelling. 



Fluids are able to travel not only upwards through the 

 wood and downwards through the bast, but there are many 

 cross-currents as well, especially through the thin plates 

 of tissue, the medullary rays, passing from pith to cortex. 

 In some stems these tissues become loaded with food- 

 materials carried to them from leaves and other parts. 

 This is seen very clearly in the Clematis. Obtain a piece 



Fig. 54. 



Ligatured Stem 



of the Rose. 



Here nutrient 



