150 GREEN PLANTS AS FOOD MAKERS 



cells, through which liquid food passes into the blood. The 

 process of absorption in animals is not entirely understood, but 

 it takes place largely by diffusion and osmosis. Without these 

 processes we would be unable to use most of the food we eat. 



Self-Testing Exercise 



In liquids and gases (1) of substances tend to pass from a 



place where they are more (2) to a place of less (3) 



by means of (4). If this takes place through a (5) 



(6), osmosis is said to take place. Substances in the 



(7) pass with the water through the (8) (9) 



into the (10) ....... .(11). 



PROBLEM V. WHAT OTHER PURPOSES DO ROOTS SERVE? 



Besides the purposes of anchorage and water absorption roots 

 have other functions. They absorb oxygen as well as water from 

 the soil into which they reach. The rows of dead trees around a 

 pond that has been raised by damming indicates that one cause 

 of the death of these trees was lack of oxygen. They were actually 

 drowned. The so-called " cypress knees," projections of the roots 

 from cypress trees, which grow in water, are adaptations to obtain 

 oxygen, as they are not found on cypress trees living in dry 

 localities. Food is stored in fleshy roots, like the carrot, turnip, 

 or parsnip. Such stores of food enable the plants that produce 

 seeds every other year (biennials) to get an early start the second 

 year from this stored food. Some plants like the ivy produce roots 

 on the stem, which help it in climbing. Such roots are called ad- 

 ventitious. Another type of air roots is found in tropical plants, 

 such as orchids. These have thickened roots with the special 

 function of absorbing and holding water. Some plants, such as 

 the strawberry, or couch grass, develop new plants by taking root 

 wherever the reclining stem happens to touch the ground. Still 

 another type of root is seen in the dodder, a parasitic plant. The 

 root of this plant pushes its way into the stems of certain plants 

 from which it absorbs its food. 



