520 Reed . — The Vahte of Certain Nutritive Elements 
cultures where sodium had been substituted for potassium than where 
neither one was present. The plants appeared to have obtained sufficient 
potassium from the glass vessels to enable them to grow and form 
chloroplastids, but they were devoid of starch. 
Selecting a dish containing prothalli growing in a solution containing 
neither potassium nor sodium, and hence devoid of starch, I added a few 
drops of a i per cent, solution of potassium phosphate. When examined 
eleven days later, they were found to contain a large amount of starch. 
This experiment also goes to demonstrate the necessity of potassium for 
the formation of starch in the cell, although that cell may contain healthy, 
growing chloroplastids. 
While it would be unsafe to apply in toto the conclusions obtained 
from the study of marine Algae to that of fresh-water Algae, it is interesting 
to note the results of Arber (’01 a). This investigator reported that sodium 
salts (preferably the chloride) are necessary in order for the formation of 
starch in Ulva latissima. The presence of potassium chloride seemed to 
inhibit almost completely the formation of starch, especially if present in an 
amount greater than that of normal sea water. 
When Hydrodictyon was cultivated in solutions lacking potassium, the 
harmful effects were more evident on the protoplasm than on the starch- 
forming powers of the cell. When neither potassium nor sodium was present 
the cells lived longer than where sodium was substituted for potassium. 
In the injured cells the protoplasm often had the form of a reticulum on 
the inner surface of the cell-wall. Usually the reticulations began to form 
at the end of a cell, and often formed simultaneously in two or three cells 
which abutted upon each other. The application of iodine solution showed 
the presence of erythrodextrin in cells which had died, and considerable 
amounts of starch in cells which were still alive. 
Cells of Basidiobolus ranarnm cultivated on potassium-free media 
exhibited protoplasmic structures which were distinctly more vacuolate 
than those of the control cultures. The nucleoli were less distinct than 
those of the control cultures. 
In another experiment Zygnema filaments were cultivated in solutions 
lacking potassium. The pyrenoids of the chloroplasts rapidly lost their 
starch, and at the end of eight weeks the chloroplasts themselves showed 
signs of serious injury. The chloroplasts had become intensely vacuolated 
and the radiating fibrillae of protoplasm which normally suspend them had 
disappeared. 
Instructive results were obtained from the study of cells which had 
been stimulated to divide karyokinetically in the absence of potassium. It 
is well known that cells in the filaments of Spirogyra may be stimulated to 
divide by exposing them to a low temperature in the dark, and then 
transferring them to optimum conditions of heat and light. The cultures 
