A DAY IN THE LIFE OF A PLANT 21 



material collected bv the roots from the soil and air, 

 are manufactured into the finished products required 

 for building up the structure of the plant. 



The green colouring matter in the leaf consists 

 of chlorophyll grains, and these grains are capable 

 of moving about at will in the cells; thus, in dark- 

 ness, they range themselves round the wall of the 

 cell, and in dull weather round three sides of the 

 cell only. 



The under surfaces of the leaf are furnished 

 with breathing pores, called stomata. As many as 

 100,000 of these pores occur on every square inch 

 of leaf surface; they permit of the transpiration of 

 superfluous moisture, and of the absorption of 

 carbon dioxide gas (CO2). 



They really act as safety valves to the cells, 

 opening when there is a superabundance of water, 

 and closing again when there is a shortage of mois- 

 ture, so as to prevent the cells being emptied of their 

 contents. 



Some plants have their epidermis, or outer skin, 

 covered with hairs, and these hairs have a special 

 office to perform. On cold, windy days, or in very 

 dry weather, they lie close over the stomata, to 

 prevent transpiration, and also to keep a layer of 

 warm air over the epidermis. 



The health of the plant depends largely on the 

 working of these stomata, and that is one reason 

 why plants in towns and cities often fail to thrive, 

 because the stomata become choked with soot and 

 dust. This should show us a very practical applica- 

 tion to gardening, pointing out how very necessary 

 it is to keep the leaves clean and healthy, that 

 they may breathe properly, and carry on without 



