THE BOOK OF NATURE STUDY 



chlorophyll " fixes/' as it is said. That oxygen is given off by a 

 plant engaged in carbon assimilation is easily shown on a bright 

 sunny day. The experiment is best tried with a water-plant such 

 as Elodea. The plant should be placed in a glass jar of water 

 under a funnel. Over the funnel, invert a test-tube full of water, 

 holding it under the water whilst placing it in position. If the 

 light is intense enough, in less than an hour bubbles of gas will be 

 seen passing up from the plant and collecting at the top of the 

 test-tube. In fact, if the apparatus is placed on a lawn in bright 



sunlight, the whole test-tube may become 

 full of gas in a couple of hours or so. 

 The rapidity with which carbon assimila- 

 tion goes on depends on the intensity of 

 the sunlight. One more thing must be 

 remembered. The carbon dioxide is taken 

 into the leaf through the stomata which 

 are present in numbers on the under sur- 

 face and sometimes also on the upper 

 surface. In Fig. 28 they will be seen on 

 the under surface. If the under surface 

 of a leaf is smeared with vaseline, the 

 carbon dioxide cannot enter and the 

 plant does not make starch. Stomata 

 may get choked up with dust, and then 

 FIG. 30. Apparatus to show the plant does not thrive. This is the 

 evolution of oxygen during reason that palms kept indoors ought to 



have their leaves washed about once a 

 week. 



Starch grains are solid bodies, insoluble in water. These 

 solid grains cannot pass through the cell walls, therefore the 

 starch is converted into a soluble substance of the nature of 

 sugar, and can then pass through the cells of the stem into the 

 root, or underground stem, where it is stored up. The carrot 

 and potato are instances of this. The grains of the cereals, wheat, 

 rice, maize, all have a good deal of starch in them. 



By the seaside or in sandy situations, plants will be found 

 with very much reduced leaves, sometimes with none at all. In 

 these cases, a couple of rows of cells will be found under the 



assimilation. O, bubbles of 

 oxygen. 



