SPECIALIZATION IN HIGHER PLANTS 



71 



•2L travels 



oe- 



down to especially adapted layers of cells in the stem or in the 

 cortex of the root, for storage in the form of starch granules, oil 

 globules, and protein crystals. Turnips, parsnips, and radishes are 

 used by people for food because of the extra plant food stored 

 in them. In the case 

 of the potato, the 

 extra food is stored in 

 an underground stem ; 

 in asparagus, sugar 

 cane, and rhubarb, it 

 is stored in stems 

 above the ground. 

 When the plant needs 

 food, a protease, 

 lipase, and amylase 

 secreted in the cyto- 

 plasm of the cells that 

 store food, change the 

 stored materials again 

 to a soluble form. 

 These dissolved foods 

 are then distributed 

 by means of the ducts. 

 Supporting cells are 

 usually found in con- 

 nection with the ducts 

 and sieve tubes. 

 These woody fibers 

 support the plant. 

 Those in the lower part of the plant strengthen the roots and 

 help to anchor the plant in the ground. The woody fibers of 

 the stems help hold up the leaves and enable them to get sun- 

 light which is necessary for photosynthesis. 



There are pathways through which fluids pass up and down 

 in plants. Raw materials travel up the stem into the leaves. 

 Food manufactured in the leaves travels down to the roots. 



