528 Reed . — The Value of Certain Nutritive Elements 
directly on the antagonistic action of calcium and magnesium which was 
discovered by Boehm (75) and investigated thoroughly by Loew (’9.2). In 
my study of the role of calcium in Vaucheria, some evidence was obtained 
upon this question which is conclusive enough, so far as it goes, to warrant 
mention in this place. On April 5 a series of cultures of this alga was 
'made in nutrient solutions lacking calcium and also in o-i per cent, solutions 
of calcium nitrate and of magnesium sulphate. The substitution for calcium 
salts in the formula of Beijerinck was made in two ways. In the first, 
magnesium chloride was substituted for calcium chloride, thus increasing 
the amount of magnesium about 50 per cent., and at the same time 
removing the antidoting agent, calcium. In the second, sodium chloride 
was substituted for calcium chloride. This solution may be considered 
as being quite different physiologically from the first because sodium, as 
was shown by the work of Kearney and Cameron (’02), acts as an antidote 
for magnesium. The filaments selected for these cultures were in a healthy 
growing condition, and contained a copious amount of oil droplets. In 
a few cases there were incipient zoosporangia at the tips of the filaments. 
At the end of eleven days there were evidences of injury to the plants 
in the solutions lacking calcium salts. The injury was found to be far 
greater in those solutions in which magnesium had been subsituted for 
calcium. There, many of the filaments were dead and broken up. The 
chloroplastids had lost their green pigment, and no oil droplets were to 
be found. The cultures in which sodium had been substituted for calcium 
contained material which was still living, although more or less injured. 
The chloroplastids were still green, and the protoplasm contained some oil 
droplets. In the control cultures there were numerous incipient oogonia 
and antheridia, but no signs of either were noted in the calcium-free 
solutions. I ultimately succeeded in keeping Vaucheria alive for seven 
weeks in cultures in which sodium had been substituted for calcium. 
In the o*i per cent, solutions of calcium nitrate, the filaments were 
healthy and showed signs of growth by their numerous oil droplets and 
bright green colour. The incipient zoosporangia in these cultures had 
developed so far as to form the transverse walls separating the contents 
of the sporangium from the rest of the filament. The contents of the 
sporangia had, however, failed to develop zoospores. The filaments in this 
solution were developing sexual organs pari passu with the controls. In 
contrast, I found that all the filaments in the o-i per cent, solution of 
magnesium sulphate were dead. 
It appears from these experiments that a large part of the injury was 
due to the toxic action of the magnesium, as well as to the absence of 
calcium. It seems reasonable to conclude that calcium is beneficial not 
only because of its value as a plant-food constituent, but on account of 
its power to antidote magnesium. This view is further supported by the 
