FUNCTIONS OF THE ESSENTIAL ELEMENTS 



i:» 



rapidly with nitrogen are also more easily attacked by fungi. 

 The cause is due not only to a cell wall less resistant to the 

 passage of the fungous hyphse, hut also in all probability 

 to a change in the composition of the cell sap which is more 

 favorable to the growth of the fungi. 



Fig. 10. 



-Effect of nitrogen on leaf development. Rape. 

 Jar 12, nitrate. Wisconsin Station. 



Jar 5, no nitrate. 



44. Sulphur. — (a) This is a necessary constituent of most 

 proteins, (b) It is also a part of some of the flavoring oils 

 in mustard, onion, cabbage, and horseradish. 



45. Calcium. — (a) Like potassium, calcium has some 

 part to play -in the solution and transportation of starch, 

 probably by forming a proper medium for the activity 

 of the amylases, (b) It also takes part in the development 

 of strong cell walls, and numerous root hairs, (c) It serves 

 as a base to precipitate oxalic acid which is formed during 

 respiration and some other activities (Section 28), and which 

 is poisonous to the plant if allowed to accumulate. Crystals 

 of calcium oxalate occur frequently in plants (Fig. 3, d). 



