96 PLANT PHYSIOLOGY 



found in quantity only in the lycopods. * It is doubtful 

 whether aluminum is necessary or even useful for these 

 plants. 



The essential soil ( ash ) constituents, as shown by water- 

 culture, are salts of phosphorus, sulphur, potassium, cal- 

 cium, magnesium, and iron. Calcium seems to be un- 

 necessary for fungi, though indispensable for higher 

 plants. 



.Phosphorus is a constituent element of protoplasmic 

 matters. In the nucleins it may amount to 6%. According 

 to Wolff's analyses,! phosphoric oxide (PjOJ constitutes 

 about one-third of the ash obtained from embryonic tissue. 

 This tissue is rich in protoplasmic matters. In older tissues- 

 containing a smaller proportion of protoplasmic matters, 

 and in dead and emptied cells, the amount of phosphorus 

 compounds is much less. In the total dry weight of a 

 plant, the amount of phosphorus, calculated as phosphoric 

 acid, is slight. This is shown by the following figures — t 



in lupine seeds 1.63% 



straw O.aOjg 



" potato tubers 0.63% 



" wood of trees 0.05% 



Though the percentage of phosphorus in the body of an or- 

 ganism indicates the degree to which it is used, it by no 

 means indicates the degree in which it is needed. Without 

 phosphorus, protoplasm could not exist. 



The source of phosphorus for the majority of plants is 

 the phosphates in soil and water. Other plants under 



* Pfefter, W. Pflanzenphyslologie, I., p. 432, Engl, transl. I., p. 437. 

 L. Chaimecyparissus and L. AJpinum have 22-27% aluminum In the ash, 

 while L. phlegmnnu, Selaginella, etc., contain only traces. Yoshida, H. 

 On aluminum in the ash of flowering plants. Journ. Coll. Science, Im- 

 perial University, Tokio, 1887. In analyses of rice, wheat, oats, beans, 

 etc. the Al. varies from 0.05% to 0.27% of the ash. 



f Quoted from Versuchsstationen, Bd. 30, by Pfeffer in his Pflanzen- 

 physiologie, I., p. 407, Eng. transl. I., p. 414. 



} Frank, A. B. Lehrbuch der Botanik, Bd. I., p. 587. Also in reports 

 of State Agricultural Experiment Stations, etc., similar figures may be 

 found. 



