378 PLANT PHYSIOLOGY 



librium between the weight of the spike and the resistance of 

 the culm that carries it. Insufficient thickening of the culm 

 and a weak development of its mechanical elements are often 

 the consequence of excessive tillering and overdevelopment of 

 the leaves caused by an abundant supply of water, which leads 

 to a thick stand and shading of the plants. Deficiency of light 

 promotes an excessive elongation of the shoots and insufficient 

 development of the mechanical tissues, thus creating conditions 

 that favor lodging. 



Likewise, lodging may be stimulated by excessive fertilization, 

 especially with nitrogen. Nitrogen contributes to a vigorous 

 development of the vegetative organs, as well as to an excessive 

 increase in the size and weight of the spike. Lodging is usually 

 produced during occasional strong winds or rains. The weight of 

 the spike is increased by the water held on the culm and leaves, 

 and the stem bends over at its base. Lodging is more serious if , 

 the soil is saturated with water. The wet soil is not firm enough 

 to hold the roots that maintain the culm in an upright position. 



The ability to bend at the nodes, seen in the culms of cereals, 

 allows the lodged plants to raise their spikes and to recover from 

 the harmful consequences of lodging. However, the yield is 

 always somewhat decreased, especially if the field is infested with 

 weeds. Cutting and binding lodged and entangled grain is very 

 difficult, and the losses during harvesting are greatly increased. 

 There are certain methods used for the control of lodging. The 

 plants are sown less thick; the application of nitrogen fertilizers 

 is reduced; and excessive irrigation is avoided. Under conditions 

 where lodging may be expected, varieties that possess a firm 

 culm and that are resistant to lodging should be chosen. 



89. Injury to Plants from Excess of Salts. Physiological 

 Peculiarities of Halophytes. Alkali Resistance of Crop Plants.^ 

 In regions of low annual rainfall, the amount of water precipitated 

 is insufficient to wash out all of the mineral salts released in the 

 processes of weathering, and the soils gradually accumulate 

 them. The rain water flowing into depressions accumulates the 

 salts from the surrounding surface, and evaporation leaves the 

 salts in the soil. Such an excessive accumulation of salts is 

 harmful to most crop plants, and in such depressions and salty 

 spots they develop less vigorously. Extremely large accumu- 

 lations of salt on so-called ''alkali soils" makes them quite 



