to the Plant Cell . 
507 
lation of nitrate nitrogen. Experimental data verified such an assumption. 
Leaves which were supplied with calcium salts were able to assimilate 
nitrates, but where no calcium salts were furnished the nitrate remained 
unaffected. 
Schimper (’ 88 ) concluded from a study of the green parts of the 
plant that the principal function of calcium was to precipitate oxalic acid 
and soluble oxalates. As the same author found (Schimper, ’90) in a sub- 
sequent research that calcium is not always present in the meristem, he 
assumes that potassium may sometimes take the place of calcium in 
neutralizing oxalates. 
Groom (*96), from a study of interrupted carbohydrate translocation 
in the absence of calcium, concluded that the presence of acid potassium 
oxalate is inhibitory to the action of diastase. This hypothesis is 
strengthened by the observation of Hammersten (’96) on the need of 
calcium salts for the formation of blood clots. Calcium salts appear to 
play a specific part in forming blood clots which is hindered by the alkali 
oxalates. It is quite possible that this action stands in the closest relation 
to the formation of the fibrin ferment. 
Additional data have recently been presented by Grafe and von 
Portheim ( 5 06), which confirm the idea that part of the injury caused by 
the absence of calcium is due to the interference in carbohydrate transfor- 
mation and transfer. These investigators found that the addition of 
levulose, dextrose, or saccharose to calcium -free solutions enabled Phaseolus 
plants to live in them for a longer period than in calcium-free solutions 
containing no sugars. 
Kraus (’97) brought out evidence on the other hand that the import- 
ance of calcium does not depend primarily upon its power to precipitate 
soluble oxalates since some plants are able to tolerate the presence of 
oxalic acid in their tissues. He found that the supply of calcium oxalate 
in the rhizomes of certain plants was drawn upon when other sources of 
calcium were gone. Loew ('98) also doubted the necessity of calcium to 
neutralize oxalic acid ; but Bruch (’02) has gone farther and shown that 
the Gramineae and some other plants can endure relatively large amounts 
of oxalates. Between concentrations of 278 and 18 parts per million of 
oxalates wheat plants grew to the period of blossoming (seven weeks). In 
that length of time all the oxalates furnished them had vanished, although 
it is possible that micro-organisms in the cultures may have aided in their 
destruction. He found that wheat could be grown in distilled water con- 
taining calcium oxalate and in nutrient solutions where calcium sulphate 
was replaced by calcium oxalate. 
In view of these facts the necessity of calcium to neutralize oxalic 
acid does not seem to be as imperative as was held by Schimper, Groom, 
and others. 
O o 3 
