inner l)ark is the process referred to when the descent of sap is 

 mentioned. 



1 1 . The food from the air and tlic food from the soil unite in the 

 livi)ig tissues. — The sap constantly passing upward from the 

 roots during the growing season is made up largely of the soil 

 water along with the salts which have been absorbed in dilute 

 solutions. This upward-moving sap is conducted largely by cer- 

 tain tubular cells of the young wood or of the woody bundles. 

 These cells are never continuous tubes from root to leaf ; but the 

 water passes readily from one cell to another in its upward courvSe. 



The upward sap gradually passes to the growing parts, and 

 everywhere in the living tissues it meets the liquid product 

 returning from the leafy parts. Under the influence of the liv- 

 ing matter of the plant, this product from the leaves first selects 

 the nitrogen. A substance more complex than sugar is then 

 formed, and gradually compounds are formed which contain sul- 

 fur, phosphorous, potassium and other elements, until finally 

 living protoplasm is manufactured. Protoplasm is the living 

 matter in plants. It is in the cells, and is usually semi-fluid. 



12. Starch and other products may be stored up during o)ie 

 growing period to be used during the 7iext sea:^07i. — Although a 

 plant strives to make a full amount of growth each season, it 

 must also provide itself for developing a new- crop of leaves and 

 of fruit the next year, if it is to live more than a single season. 

 It must also provide for its offspring. Tubers (white potato), 

 stems (cacti), and roots (sweet potato) generally serve as storage 

 organs for food. Thick, fleshy, leaves, as in the century plant, 

 which live during many seasons, may also serv^e as storage organs. 



The peach tree blossoms and sets its fruit, usually, before the 

 leaves are open. In fact the food stored up one season has a 

 most important influence in determining the crop of the next 

 year. Bearing this in mind, one appreciates the value of keep- 

 ing the leaves free from fungous and insect injuries throughout 

 the growing season. 



13. Plants 7ieed oxygen for respiration, just as animals do . — 

 So far \ve have referred especially to the carbon dioxid of the 

 air. To most plants the nitrogen of the air is inert, and only 

 serves to dilute the other elements ; but the oxygen is very nee- 



