to the Plant Cell. 
53i 
be considered as the initial middle lamella. This middle layer appears to 
be formed originally by deposition from the split halves of the cell-plate, 
which were in turn derived from thickenings on the kinoplasmic spindle 
fibres. It cannot be assumed, however, that the middle lamella consists 
only of the material first deposited from the young plasma membranes. 
We have evidence rather that it consists of the material first deposited by 
the plasma membranes plus a certain amount of material subsequently 
deposited in contact with the layers. The writer believes that the absence 
of new cell-walls after mitosis, in cells lacking calcium, indicates that the 
cells were unable to form the fundamental ‘ middle layer ’ of the cell-plate, 
and, in consequence, no cell was formed. 
It appears from what has been said that the role of calcium differs in 
certain respectsfrom that of the elements previously described. It differs quite 
widely from potassium and phosphorus in forming but a small proportion 
of the actual living substance of the plant. The functions which it performs 
are varied, but are none the less specific on that account, and its absence 
may affect some of the most vital activities of the plant. Calcium influences, 
in a remarkable way, processes and products into which it does not seem 
itself to enter, although it may be necessary for the formation of the zymotic 
and other agents which accomplish the results. It is now recognized that 
calcium salts act beneficially upon the soil mainly through their ability 
to bring about the proper physical and chemical conditions for growth 
without serving directly as a nutrient. It is entirely possible that it may 
so function inside of the plant in the living substratum. 
A conspicuous example of how this function may be performed is 
in the formation of calcium oxalate. By precipitating the poisonous oxalic 
acid in an insoluble form, the juices of the plant are maintained in a proper 
condition of acidity for their most effective work. It was shown, for 
example, by Groom (’96) that diastase was unable to accomplish the normal 
conversion of starch to sugars in the presence of oxalic acid. 
It seems probable from such work as that of Wehmer (’06) that the 
plant is not altogether able to regulate the production of oxalic acid, as 
Pfefifer believes. It is, however, undoubtedly able to regulate to some 
extent the amount of calcium absorbed, and hence to control in that way 
the processes into which calcium enters. It is altogether probable that 
the amount of calcium absorbed by the plant at different times would 
be found to be subject to wide variation. 
The accumulation of lecithins and fatty substances, which I have found 
in the cell when calcium salts are lacking, is another example of an impaired 
activity in which we must believe that calcium only functions in a very 
indirect manner. The absence of egg cells and archegonia of the fern 
prothalli, and the inability of cells to form cellulose are other examples. 
