to the Plant Cell. 
5 0 -2 
3 o 
of a proper ratio between magnesium and phosphorus was of more impor- 
tance than the absolute amount of phosphorus present. 
The filaments of Spirogyra which were cultivated in solutions lacking 
magnesium continued to live for some time, but showed characteristic 
injury. At the end of five weeks I found the chlorophyll bands disarranged 
and forming a more or less compact mass near the centre of each cell. 
A typical cell is represented in Fig. 2 . In the cells which showed less 
injury, the nuclei were imprisoned within the irregular mass of chloroplasts ; 
but in the more severely injured cells the nuclei had often lost their proto- 
plasmic fibrillae and could be found in various abnormal positions in the 
cells. The state of affairs would seem to indicate that the fine strands of 
protoplasm radiating from the nucleus to the chloroplasts had been acted 
upon by some agent which caused them to contract simultaneously. In 
Fig. 2 .-Spirogyra cell grown six weeks in magnesium-free solution. Shows the 
contraction of the chloroplasts away from the ends of the cell. Drawn from a living 
cell mounted in water. 
most cases the contraction had been violent enough to draw the chlorophyll 
bands away from the ends of the cell, and to make a more or less compact 
mass in the centre of the cell. 
From a study of their behaviour it seems correct to ascribe the effects 
produced to the calcium present which is, in the deficient solutions, 
unbalanced by magnesium. Such an effect has at least an analogy, and 
perhaps more, in the effect of calcium on the muscle of animals. It has 
been shown by Greene (T9) and by Howell (’01) that strips of heart muscle 
will give a characteristic series of beats when placed in an isotonic solution 
of sodium chloride. A solution of calcium chloride, on the contrary, 
increases the tonus of the muscle which may pass into a state of permanent 
rigor from which recovery is impossible. 
The chlorophyll bands in these cells were narrow, similar in many 
respects to those in cells deprived of calcium salts. The characteristic 
lobed margins were also lacking. In some cases the chloroplasts had been 
so sharply bent that they were broken at the centre, thus giving two groups 
of chloroplasts with a very narrow space between them. The pyrenoids 
stood out distinctly and appeared to be nearly, if not fully, normal size. 
There was an absence, however, of accessory pyrenoids (or dark staining 
bodies) similar to those appearing in the chloroplasts of the control plants. 
