WATER CULTURE, PHOTOSYNTHESIS, RESPIRATION. 173 



230. Translocation of Fhotosynthetic Starch by 

 Diastase. Is the disappearance of starch from a foliage- 

 leaf due to its conversion into sugar by means of the 

 ferment diastase as in the translocation of starch from 

 the cotyledons of a Bean seedling or from the endosperm 

 of a Wheat seedling ? 



In the evening of a bright day remove a number of leaves 

 from a Tropaeolum plant that has been exposed to good 

 diffused light ; dry them in an oven, and rub them up 

 with some water in a mortar or cut the fresh leaves up, 

 add some water, and squeeze out the leaf -juice with a 

 meat- juice press. Filter the extract thus obtained, treat 

 it with absolute alcohol to remove the sugar present in it, 

 and divide it into two portions; boil one portion in a 

 test-tube. Make some thin starch-paste, place it in three 

 saucers marked A, B, C. To A add some unboiled ex- 

 tract; to B, some boiled extract; leave C as a control. 

 After a time test portions of all three with iodine : in A 

 the starch is converted into sugar by the diastase in the 

 extract ; in B the diastase has been destroyed by boiling. 



231. The Giving-off of Oxygen during Photosyn- 

 thesis may be demonstrated in various ways, but is, 

 perhaps, most readily observed in submerged water-plants 

 (e.g. Elodea, Marestail, Water Milfoil). Collect some of 

 these plants, place them in a large vessel if necessary 

 tie them to a stone to keep them sunk at the bottom 

 and set the vessel in good but not too strong light. Note 

 the bubbles of gas which are given off, especially if the 

 stems are cut across and the snoots inverted when sunk 

 in the water. 



Graduate a large test-tube roughly by gumming along 

 one side of it a strip of paper marked into inches or 

 centimetres. Invert the tube so that it dips below the 

 surface of the water in a jar, and fix it in this position by 

 means of a retort stand. 



Loosely tie a number of Elodea shoots, with thread, to 

 form a bundle, and place this in the jar, with the cut ends 

 of the shoots projecting into the test-tube. When a good 

 deal of gas has collected, slip your hand or a glass plate 



