305 



calcium. In this, the calcium may often act beneficially on the constitution 

 of the soil and often directly on the composition of the cell sap. According 

 to our explanation of the matter, a considerable number of cases of disease 

 exist which are called forth directly by nitrogen excess, and for which the ad- 

 dition of calcium and phosphoric acid remains the only effective remedy. 

 In the division "Enzymatic Diseases," we will also have to consider the 

 beneficial action of calcium fertilization. There we will also touch upon 

 the subject of the over-abundant formation of acid in the plant which cer- 

 tainly sometimes influences unfavorably the mode of production. Thus, 

 for example, with a lack of calcium in the soil, the sap of sugar cane con- 

 tains a great deal of acid and but little sugar\ We will mention later special 

 cases of oxalic acid poisoning. 



e. Changes Due to a Lack of Magnesium. 



Plants grown in a nutrient solution lacking magnesium often live longer 

 than when the nutrient solution does not contain calcium. It might be con- 

 cluded from this that the plant is able more easily to remobilize the mag- 

 nesium compounds already deposited in its tissues and to make them partially 

 accessible again for the young organs. If the grain becomes diseased slowly 

 from magnesium hunger, the leaves are a light green and appear limp, but 

 not directly wilted. From the beginning it is possible to imagine a very 

 considerable effect on the formation of seeds, if one considers that, for ex- 

 ample, the globoids enclosed in the protein grains may be assumed to be 

 calcium and magnesium compounds of a double phosphoric acid. In 

 reality, with a lack of magnesium, there is a decrease in the formation of 

 fruit, as stated by Nobbe-. He gives the following symptoms. The leaves 

 become pale in color, with yellow to orange red spots here and there. 

 The chlorophyll grains are pale yellow green and contain, as a rule, small 

 amounts of starch. Diminished cell division is noticeable in the epidermis. 

 Nobbe found that plants grown with a lack of magnesium correspond to 

 those from nutrient solutions free from nitrogen, in that red spots are 

 present on the petioles and the leaves fall prematurely. The latter character- 

 istic may well be present in all starved plants, since the young organs ex- 

 haust the older ones when the supply of nutriment is insufficient. 



Moller^ also observed an orange red coloring in his cultivations of 

 Scotch pine seedlings with a lack of magnesium. He says that the needles 

 in October had bright orange yellow tips but farther back passed through 

 a bright red zone into a normal green one. The discoloration appeared 

 when the seedlings had been given magnesium in the second year. 

 Ramann analyzed the orange tipped needles of two-year old Scotch pines 

 and found that these contained 0.2791 per cent, magnesium (calculated on 

 the dry weight), while the adjacent normally green specimens showed a 

 content of 0.6069 P^r cent. 



1 Semler, Tropische Agrikultur. II Edition. Vol. Ill, p. 236. 

 ^ Dcibner's Botanik fiir Forstmanner, edited by Nobbe. 4th Edition, p. 315. 

 ■■! Moller, A., Karenzerscheinungen bei der Kiefer. Sond. Z. f. Forst- und Jagd- 

 wesen, 1904, p. 745. 



