OSMOSIS 



I8i 



Ex. 101. — Cut a few slices, about J of an inch thick, through a beetroot 

 or sugar beet ; wash them in distilled water and place — 

 (i) Some in a vessel in distilled water. 



(2) Others first in boiling water for a minute or two to kill the cytoplasm 

 of the cells, and then into a vessel containing distilled water. Allow them 

 to remain for four hours ; afterwards take out a small quantity of water 

 from each vessel and test for sugar by boiling with a drop or two of 

 hydrochloric acid and subsequently adding Fehling's solution (see Ex. 80). 



Ex. 102. — Cut a transverse section through a portion of a garden beetroot. 

 First wash it in water in a watch-glass, and then mount in water and 

 examine with a low power of the microscope. 



( i) Observe the presence of pink cell-sap in the uninjured cells ; note that 

 it does not escape into the surrounding water. 



(ii) Run under the cover-glass a few drops of a 4 per cent, solution of 

 common salt, and observe that as the colourless solution of salt penetrates 

 into the cell plasmolysis begins and the cytoplasm recedes from the cell- 

 wall. Ivotice that although water is withdrawn through the cytoplasm, the 

 latter does not allow the colouring matter of the cell-sap to 

 diffuse outwards, for the salt-solution which passes inwards 

 through the cell-wall remains uncoloured. 



(iii) Remove the cover-glass when the cells have become 

 plasmolysed, wash away the salt-solution by soaking the 

 section for a second or two in pure water, and then re- 

 mount in water. 



Examine with microscope and note that the cytoplasm 

 gradually recovers its original position close to the cell- 

 wall. 



Ex. 103. — Cut a similar section of a piece of beetroot, 

 and dip it for a moment into methylated spirit to kill 

 the cytoplasm of the cells ; wash quickly and then mount 

 in water ; note that the pink cell-sap now diflFuses out into 

 the surrounding water. 



Ex. 104. — Make careful measurements of portions 2 or 

 3 inches long of the young primary roots of beans and 

 peas, young hop shoots, young flower-stalks of a dandelion, and other turgid 

 portions of plants. Place them in a 10 per cent, solution of salt for six or 

 seven hours and measure again ; note the shrinkage and flabbiness of the 

 parts due to loss of turgidity of the cells. 



Ex. 105. — Cut off a shoot of a Jerusalem artichoke and leave it to wither 

 in an ordinary room for about an hour; note the limp state of its leaves 

 after that time. After cutting off half an inch of the stem fasten it to a 

 bent glass tube by means of a short piece of rubber tube (r) as in Fig. 83. 



Fig. 83 



