WORK OF THE SHOOT 85 



account for the carbon dioxide taken in and the oxygen 

 given out during photosynthesis. Six molecules of formalde- 

 hyde are now supposed to combine to form sugar. By 

 further action the sugar is deprived of a molecule of water 

 and is converted into starch. Another possible explanation 

 is that during sunlight chlorophyll is continually breaking 

 down and re-forming, and formaldehyde may be one of the 

 products formed as a result of the decomposition of the 

 chlorophyll. This building up of starch grains is intimately 

 associated with the chlorophyll corpuscles, but when formed, 

 they become detached and lie in the cavity of the cell. 

 These grains, however, are solid, and, as we have learnt 

 from our experiments in osmosis, are quite incapable of 

 being transferred from cell to cell in this form. Obviously, 

 if the grains are not removed, the cell will soon reach its 

 limit of activity in this direction. 



Starch digestion. The following experiments will help us 

 to understand how the transference of food-materials is 

 brought about. Place a little potato starch in a beaker, add 

 water, and note that the starch grains are not dissolved. On 

 boiling the liquid for a few minutes, a mucilage is produced, 

 but the starch does not completely dissolve. Dilute this 

 with cold water. Place a little of the cooled liquid in a test 

 tube, add saliva from the mouth, mix thoroughly, and keep 

 it at the temperature of the body for fifteen or twenty 

 minutes. This may be conveniently done by enclosing the 

 tube firmly in the left hand while the following experiments 

 are carried out. To another portion of the weak mucilage 

 add a little diastase or malt-extract (which contains 

 diastase), and allow it to stand at the temperature of the 

 room for twenty minutes or more. In the meantime take 

 another test tube and place in it a little grape-sugar, add 

 water to it, and note how readily the sugar dissolves. Take 

 a small portion of this, test it with iodine solution, and 

 note that no violet coloration results. To the remaining 



