

xi ABSORPTION AND MOVEMENT OF WATER 149 



along the sieve tubes of the phloem, and from cell to cell by 

 osmosis, to those parts of the plant where they are needed. 



The carbohydrates (sugars) travel in solution along the 

 parenchyma cells which surround the vascular bundles in the 

 leaf and belong to the cortex of the stem. 



The needs of the various parts of the plant cause the current 

 to move to those places where material is being used up in 

 the formation of new cells, or is being stored up as reserve 

 material. 



EXPT. 142. From the plant used for Experiment 140, cut away 

 from a branch a ring of tissue so as to remove the phloem. Note 

 The branch below the cut will not increase in size unless elaborated sap 

 is brought from some other part of the plant, and, as a rule, this does 

 not take place. 



EXPT. 143. Remove a branch from a woody plant, such as the 

 Beech, and at about nine inches from the base remove a ring of 

 tissue down to the new wood. Place the branch in water. Remove 

 another branch, and place it in water without injurying it. Note 



(i) New roots are produced from the portion of the stem above the 

 place where the ring of tissue has been removed. 



(ii) No adventitious roots are produced from the portion below the 

 wound, because no elaborated sap can pass through the wound because 

 it can only travel through the phloem, and this has been removed. 



(iii) The branch from the tree which was placed -in water without 

 being injured produces roots from the tip of the stem. 



SUMMARY. 



Absorption of Water and Minerals. All materials (with the exception 

 of carbon} which plants require for their growth are taken in by the 

 root-hairs and uncuticularised portions of the root. 



Absorption. That roots absorb is shown by placing the roots of a 

 plant in a solution of eosin, when their internal parts are stained. 



Osmosis. The mixing of fluids through a permeable membrane is 

 called osmosis ; for osmosis to take place it is necessary for the fluids to 

 have different densities. 



The sap given out by roots can dissolve some of the insoluble con- 

 stituents of the soil. 



Conditions necessary for Absorption. 



(1) The air surrounding the plant must have a certain temperature. 



(2) The soil or solution in which the plant is growing must also have 

 a certain temperature. 



(3) The strength of the solution has a decided effect on absorption. 

 Plants give out Moisture. Places with a prolific vegetation have a 



moist atmosphere. An Oak tree gives out many gallons of water on 



