Factors Affecting Growth and Reproduction 217 



or structures. These non-essential elements, however, may 

 greatly affect the growth of plants. When present in small 

 amounts they may be favorable to the plant, but when present 

 in larger amounts they may be injurious. 



Nitrogen enters into the composition of all proteins and of 

 many related but less complex compounds, like chlorophyll, 

 amino acids, and alkaloids. Carbohydrates furnish the basis of 

 these compounds, and both carbohydrates and proteins enter 

 largely into the making of protoplasm. Hence, when there is an 

 abundance of carbohydrates and nitrogen, vegetative growth is 

 greatly increased. This condition may be seen especially in 

 potatoes. If too much nitrogen is available, the plants develop 

 enormous tops but produce almost no tubers, because as fast as 

 carbohydrates are made nitrogen is available for the production of 

 proteins and protoplasm and further growth of the shoots ensues. 

 If the amount of nitrogen is just sufficient for the growth of an 

 average potato plant, there will be an excess of carbohydrates 

 formed, and these will accumulate in the tuber as starch. This 

 example illustrates what is meant by the proper balance of 

 carbohydrates and nitrogen. 



Another example of the carbohydrate-nitrogen balance may 

 be seen in wheat. If the proportion of nitrogen is too large, the 

 wheat grows tall and the straw is so weak that it falls over, and 

 the grains fail to accumulate the usual amount of starch. Carbo- 

 hydrates form the cell walls, and if they are all consumed in 

 extending the stems and leaves, there are none left for thickening 

 the cell walls, upon which the stiffness of stems depends, and none 

 for filling the grain. Too much nitrogen added to orchard soils 

 leads to great vegetative growth and very little fruit. In- 

 sufficient nitrogen leads to poor growth and few blossoms, and the 

 fruit is small and woody, because the excess carbohydrates 

 accumulate as starch and cellulose. 



Calcium occurs in many plant cells in the form of calcium 

 oxalate crystals. These may be large, rounded masses occupying 



