522 Reed . — The Value of Certain Nutritive Elements 
one solution to another was made at the time the cultures were taken from 
the refrigerator, and just before submitting them to optimum conditions. 
Seven and one-half hours later, I found upon examination that a few cells 
had undergone division. Evidently there had been sufficient stimulus in 
merely transferring the cells to a different solution to induce a few cases 
of division, although no potassium salts had been given by the transfer. 
Whether the stimulus was of a physical or chemical nature remains to be 
determined. 
The effect of adding a salt of potassium to cultures in which the cells 
were unable to divide in consequence of a previous lack of potassium was 
noted upon some of the material just described. At the time of removing 
the material from the refrigerator, a few drops of a 2 per cent, solution of 
potassium phosphate were added to one of the cultures. Seven and one- 
half hours later I found that there had been some cell-divisions accom- 
plished, but that many (perhaps a majority) of the cells had remained 
undivided, although they plainly showed the effect of the stimulus. This 
may have been due to one of two reasons. Potassium might have been 
necessary for certain of the initial processes and, lacking that, the whole 
mechanism of mitosis came to rest. Again, the failure to divide may have 
been due to lack of surplus nucleo-proteid material, and in the time of the 
experiment the cells were unable to use the new supply of potassium to 
form the requisite amount of nucleo-proteid. 
2. Experiments upon the role of phosphorus. 
A suitable supply of phosphorus is of fundamental importance for the 
continued activity of every living cell. Growth does not occur in the 
absence of phosphorus, because it is of primary importance for the forma- 
tion of proteids. Koch and the writer have shown (Koch and Reed, ’ 07 ) 
that when only an insufficient amount of phosphorus is present, the 
phosphorus of the nucleo-proteids shows practically no percentage decrease, 
while the water-soluble forms of organic and inorganic phosphorus show 
a relatively great decrease. The same conclusion may be drawn from 
the extensive analyses recently published by Wilfarth, Romer, and Wimmer 
(’ 05 ). They have shown that the amount of P 2 0 5 in barley straw per 
hectare decreased from 29-04 kilograms on June 17 to 9-59 kilograms on 
July 27. The amount of P 2 0 5 in the grain per hectare increased from 
3-54 kilograms on June 17 to 29-84 kilograms on July 27. These results 
indicate that the nuclein phosphorus of grains increases in amount at the 
expense of the water-soluble forms of phosphorus in the straw. 
Phosphorus is also necessary for the formation of the glycero-phosphoric 
acids, of which lecithin is one of the best known, and which is present in 
nearly every living cell. The physiological importance of lecithin for 
plants has been pointed out by Loew (’ 99 ), Overton (’ 00 ), and others. 
