37 



1st. How will the plant comport itselt in a solution containiii<>' all tbe 

 ingredients necessary to its growth except potash, and what will be the 

 explanation of the peculiar i)henoinena that may be manifested ? 



2d. How will the plant comport itself in solutions, each containing 

 potash, but in difierent forms of combination, (as chloride, sulphate, 

 phosphate,) and what are the causes ■ of the relatively more or less 

 favorable effect of these salts ? 



3d. Can sodium or lithium replace potassium in the performance of 

 its physiological functions ? 



The method of water-culture was used for the experiments. 



Plants were cultivated in various solutions. One, the " normal solu- 

 tion," contained all the essential ingredients, including chloride of potas- 

 sium. In a second, potash was omitted ; in a third, it was supplied as- 

 nitrate ; in a fourth, as sulphate; in a fifth, as phosphate, while in others 

 it was replaced by salts of sodium and lithium. In the normal solutions 

 the plants grew normally, and reached a height of several feet. With- 

 out potash the plants were only a few inches in height, and micro chemi- 

 cal investigation showed that there was no proper formation of starch 

 in the leaves, a fact of which their stunted growth was an obvious 

 result. The p enomena observed in the development of the different 

 plants were very interesting. The general result of the experiments^ 

 is expressed by Nobbe as follows : 



1st. In a solution containing all the nutritive ingredients except 

 potash, the plant grows as in pure water. It cannot assimilate the 

 materials needful for its growth, and shows no. increase in weight, be- 

 cause, without the co-operation of potash in the chlorophyll grains, no 

 starch is formed. 



2d. The chloride is the most efficient form of combination in which 

 potassium can be furnished to the buckwheat plant. jSTitrate of potash 

 stands next. If the potassium be given only in the form of sulphate or 

 phosphate, there appears sooner or later a very marked disease, which 

 is due to the fact that the starch which is formed in the chlorophyll 

 grains is passively accumulated in the leaves rather than carried 

 away to be utilized in the development of the plant. 



3d. Potassium cannot be replaced physiologically by sodium or 

 lithium. While the sodium is simply useless, lithium, in the cellular 

 fluid, has a positively injurious effect upon the plant-tissues. 



Similar results were obtained in the experiments with summer rye. 



It seems, then, to be reasonably well established that the co-operation 

 of potassium in the cellular fluid is requisite for the building of starch 

 in the chlorophyll grains, and hence its necessity to the growth of the 

 plant. In other words, these experiments show that at least one office of 

 potash in the plant is to aid in the formation of starch. 



Nobbe proposes, by similar experiments, to investigate the functions 

 of the other elements that make up the food of the plant. We may 

 look forward to very interesting results from studies of this sort. 



It should be borne in mind, however, that conclusions like these, 

 founded upon a particular series of experiments, are not to be univer- 

 sally applied. In this case the buckwheat plants did better with potas- 

 sium as chloride than as sulphate. Had a small amount of chlorine 

 been furnished in another form, the sulphjite might have been found 

 more efficient — indeed, practical. ' 



