178 Plant Physiology 



hypothesis respecting the role of calcium in protein forma- 

 tion. According to him we must anticipate a calcium- 

 protein compound as important in the building up of the 

 nucleus and plastids of the cell. In the absence of suffi- 

 cient calcium he believes that magnesium takes its place, 

 and that this magnesium compound does not possess the 

 necessary capacity for imbibition phenomena required by 

 the cell structures. There are some important objections 

 to be met in considering this hypothesis, in view of the 



FIG. 49. Effect of liming in the production of alfalfa ; no fertilizer (1), 

 lime only (2), andlims with nitrogen (3). [Photograph from the Rhode 

 Island Exp. Sta.] 



facts that magnesium salts are not toxic for the fungi and 

 for the lower algae, and, in the presence of small amounts 

 of calcium, relatively nontoxic also for the marine algae, 

 as well as for a few of the higher plants. 



On the other hand it is true that plants grown in solu- 

 tions lacking calcium show, coincident with the expected 

 pathological conditions, an increase in the magnesium 

 content, whereas other pathological effects produced by 

 unfavorable conditions show a normal ratio of calcium 

 and magnesium. 



