8 CHEMISTRY OF PLANT LIFE 



The final result of an ample supply of phosphates in hastening 

 the ripening process and stimulating seed production, as con- 

 trasted with that of an over-supply of nitrogen, has led to the 

 popular statement that " phosphates make seeds." This state- 

 ment, while not strictly accurate, is a fairly good summary of the 

 combined results of the role of phosphorus in the plant economy. 

 Large amounts of phosphorus are stored in the seeds. The two 

 facts that large amounts of these compounds are thus available 

 to the young seedling and that relatively large proportions of 

 phosphates are taken from the soil by the plant during its early 

 stages of growth are undoubtedly connected with the need for 

 rapid cell-division at these periods in the plant's life. 



Potassium. The popular expression that " potash makes 

 sugars and starch " is a surprisingly accurate description of the 

 role of this element in plant metabolism. Either the photo- 

 synthesis of starch, or the changes necessary to its translocation 

 (it is not yet certain which) is so dependent upon the presence of 

 potassium in the cell sap that the whole process stops at once if 

 an insufficient supply is present. The production and storage of 

 sugar, or starch, in such root crops as beets, potatoes, etc., dimin- 

 ishes in direct proportion with a decreasing supply of potassium 

 as plant food. The grains of the cereal crops become shrunken 

 as a result of potassium starvation; and are plump and well 

 filled with starch in the endosperm when sufficient potassium is 

 available for the crop's needs. 



The general tone and vigor of growth of the plant is largely 

 dependent upon an ample potassium supply; potash-hungry 

 plants, like those which have been weakened by any other unfav- 

 orable conditions, have been found to be more susceptible to 

 injury by disease, than those which are well nourished with this 

 food element. But potassium-starvation does not produce any 

 pathological condition of the cell contents; its absence simply 

 prevents the possibility of the development of the necessary car- 

 bohydrates for vigorous growth. 



There is no known difference in the availability, or effective- 

 ness, of potassium from the different forms of compounds con- 

 taining it which may be present in the soil. Apparently, the only 

 essential is that the compound shall be soluble so that it can be 

 absorbed into the plant through the root-hairs. Of course, the 

 acid radical to which the basic potassium ion is attached may, in 



