576 



SCIENCE 



[N. S. Vol. XXXVI. No. 931 



role of ealeium, we shall see that they 

 clear up many puzzles. As long as we try 

 to explain all the benefits of lime merely 

 as nutrient effects we can not account for 

 its special importance. But as soon as we 

 learn that lime is extraordinary in its pro- 

 tective action, which greatly surpasses that 

 of all other substances in the soil, its im- 

 portance becomes self-evident. This pro- 

 tective action is so great that a single cal- 

 cium ion acts as an antidote to from 20 to 

 100 ions of sodium, potassium, ammonium, 

 etc. 



To make clear that this result may be 

 quite apart from its nutritive action it may 

 be mentioned that lime is unnecessary as 

 a nutrient for many fungi, and the ordi- 

 nary nutrient solutions for these plants are 

 made up without it. But if the concentra- 

 tion of the nutrient solution be too high it 

 becomes toxic: then the addition of lime 

 overcomes this toxicity, without adding 

 any nutrient, and makes an extraordinary 

 increase in the growth of the plants. 



The great importance of protective ac- 

 tion has led to a number of attempts to 

 explain how it is brought about. It was 

 early suggested by Loeb that one salt may 

 prevent the toxic action of another by pre- 

 venting it from entering the cell. This 

 suggestion has not been put to decisive 

 experimental test until recently. The out- 

 come is extremely satisfactory: it may be 

 illustrated by the following typical case. 

 Spirogyra placed in 0.1 M NaCl solution 

 quickly died, but it lived a long time if 

 a very small amount of CaCU was added 

 (1 molecule of CaCla to each 100 molecules 

 of NaCl). In order to find out whether 

 the calcium hindered the sodium from 

 entering the cell, the plants were placed 

 in a solution of NaCl strong enough to 

 produce plasmolysis. On observing them 

 continuously under the microscope the 

 cells were seen to recover from plasmolysis, 

 the protoplasm expanding so as to com- 



pletely fill the space inside the cell wall. 

 This could only be interpreted as due to 

 the penetration of NaCl, which thus raises 

 the osmotic pressure vnthin the cell. But 

 if the Spirogyra be plasmolyzed in a solu- 

 tion of NaCl containing a little CaClj (1 

 molecule of CaClj to 100 molecules of 

 NaCl) the recovery takes 10 hours instead 

 of the half hour required when it is in 

 pure NaCl. It is therefore obvious that 

 the penetration of the NaCl is hindered by 

 the presence of CaCU. 



The same thing is shown by experiments 

 on Lammaria, in which the rate of pene- 

 tration of the ions of NaCl is directly 

 measured by electrical means. Here the 

 addition of a very little CaCU hinders the 

 penetration of the ions of NaCl in the most 

 striking way. 



It may be asked how merely delaying 

 the entrance of a salt produces a beneficial 

 effect. It is a well-known phenomenon 

 that the sudden addition of a salt may pro- 

 duce precipitation of a colloid when the 

 slow addition of the same amount produces 

 no such efi:ect. Similar facts are familiar 

 in biology. Moreover, there is good evi- 

 dence that when NaCl finally begins to 

 penetrate the cell in a mixture of NaCl -|- 

 CaCL the CaCU enters along with the 

 NaCl; it may thus hinder the NaCl from 

 entering various internal cell membranes 

 (such as the nuclear membrane). It may 

 also have other effects on the protoplasm. 



We may therefore conclude that the 

 mechanism of antagonism consists pri- 

 marily in hindering the penetration of toxic 

 substances, just as calcium hinders sodium 

 from entering the cell. That the calcium 

 does this by directly affecting the plasma 

 membrane is shown by a variety of evi- 

 dence which can not be described here. 



W. J. V. OSTEEHOUT 



Harvard University, 

 Laboratory of Plant Physiology 



