IO INANITION AND MALNUTRITION 



sium in the medium apparently increases the general vigor of growth, lengthens 

 the period of development and increases the total dry weight of the oat plant. 

 The grain production is lowered, however, the ratio of grain to straw and the 

 weight of the individual kernels being decreased. Thus the results are closely 

 similar to those of a calcium deficit. In general, the results of magnesium 

 deficiency also resemble those of etiolation, when plants are grown in darkness 

 (to be discussed later). This is probably because of the interference with 

 chlorophyll formation or function in both cases, a conclusion which is supported 

 by recent studies on the effects of magnesium deficiency in tobacco and maize 

 by Garner, McMurtrey and Moss ('22). 



DEFICIENCY IN IRON, SULPHUR OR MANGANESE 



Von Liebig ('76) recognized the necessity for a certain amount of sulphur 

 in the formation of proteins in plants, and of iron for chlorophyll-formation in 

 green plants. He stated that although only a very slight amount of iron is 

 necessary, in its complete absence the plants become yellow and stunted in growth, 

 a condition known as chlorosis. Knop ('64) had found iron necessary for the 

 growth of buckwheat and grasses in general, though apparently not for maize 

 and peas. Gile and Carrero ('16) concluded that in the absence of special 

 precautions it is often possible that the rice plant may be inhibited in its growth 

 by an insufficient supply of available iron; a view also in accordance with the 

 experience of Hoagland ('19) for the barley plant. The exact role of iron in 

 plant growth is not clear, for it does not enter into the chemical composition of 

 chlorophyll (Willstaetter). McHargue ('22) found that in sand cultures man- 

 ganese is necessary for plant growth and development to maturity. In cul- 

 tures without manganese, growth ceased in about six weeks; the plants became 

 chlorotic, with death of the young leaves and buds. 



PHOSPHORUS DEFICIENCY 



Ville ('61) was one of the first to demonstrate (in sand cultures) the indis- 

 pensability of phosphates for all plant growth. This view has been universally 

 adopted, the possible substitution of arsenic (Bouilhac '94) having been refuted. 

 Loew ('91) found that when phosphorus is withheld the cells of Spirogyra cease 

 to grow and the chloroplasts turn yellow. Starch formation continues for some 

 time, however, and fats and proteins accumulate in the cells. Becquerel 

 ('04) and Schoene ('06) found it possible to germinate moss spores in solutions 

 lacking phosphorus; but the development of the protonema is inhibited, and 

 the rhizoid system is abnormally extensive. 



Reed ('07) found that of all the elements the lack of phosphorus seems to be 

 the most injurious, its influence predominating in normal cell metabolism. 

 In the spores of moss (Atrichum) no germination occurs without phosphorus. 

 The thickness of the cellulose cell walls is increased in Basidiobolus, and in 

 Spirogyra may even be doubled. In the latter, a few cells elongate, as in the 

 K-f ree cultures, but no cell division occurs. (On adding a few drops of potassium 



