May, 1921] 



BIENNIAL REPORT. 



davipes, viredosporcs of Puccinia antirrhini and Uromyces caryophyllinus, 

 teleuto-spores of Puccinia malvacearum. 



The results obtained are indicated in the following table: 



Cardinal Temperatures of Spore Germination in Certain Rusts. 



Relation of Potassimn to Growth in Plants. — In collaboration with Mr. T. O. 

 Smith, Department of Chemistry, the work on this project was completed 

 during the year, 1919, the following being the conclusions arrived at: 



The reserve supply of potassium in the seed is not sufficient to maintain 

 normal growth except for a very short period of time. 



Symptoms of potassium starvation appear early in the life of a plant and are 

 characterized by a dwarfing of the axes and progressive death of the foliage, 

 the older leaves succumbing first. 



The potassium utilized per gram dry matter formed is higher in plants grow- 

 ing in the presence of potassium than in plants growing in its absence. 



The relative distribution of potassium per gram dry matter formed as be- 

 tween the tops and roots is the same whether the plants are growing in the ab- 

 sence of, or presence of potassium. 



Recovery from potassium starvation occurs the more slowly the longer the 

 potassium is withheld. 



The relative distribution of potassium as between tops and roots per gram 

 dry matter formed is the same whether the plants are growing in the presence 

 of potassium, in the absence of potassium, or have first suffered from a more or 

 less prolonged period of starvation. 



Where potassium starved plants are supphed with potassium, the element 

 becomes distributed promptly in accordance with the physiological needs of 

 the plant, the absorption progressing with marked rapidity. 



The amount of potassium contained in the seed does not determine the 

 length of time a plant grown from it can live in the absence of potassium with- 

 out injury resulting. 



Department of Chemistry. 

 Plant Metabolism Studies.— Nearly all of the different organs or parts of 

 plants (leaves, stems, roots, seeds, bulbs, tubers, etc.) are of economic use. In 



