es  —”S 
 t90r] _- BRIEFER ARTICLES 143 
the oxalic acid liberated. It is generally admitted that the oxalic acid 
in various plants, as Rheum, Rumex, etc., serves as a protection against 
animals, not because of its highly poisonous nature, but because of the 
extremely sour and astringent taste. 
The theory that calcium oxalate serves to keep away animals 
through mechanical interference is highly improbable for several rea- 
sons. If this were the case the crystals would be peripherally located, 
as in this position they would soonest produce the desired effect. The 
crystals actually occur about uniformly distributed through the tissues 
of the various plant organs, and are in many instances especially 
abundant in the interior, as in the spongy tissue of leaves, the pith of 
stems, and the heart wood of steins. This mechanical interference can 
have application to small animals only, such as snails, insect larvae, 
etc. The crystals could not possibly injure or repel large animals 
capable of destroying the entire plant rapidly. 
Based upon observation, the conclusion is reached that the prime 
function of calcium oxalate in plants is that of mechanical support; 
secondarily it plays the part of a reserve product as stated by Kraus. 
The following are the chief reasons in favor of the mechanical support 
t oe 
. Cells containing prismatic crystals are quite generally associated 
ia, bast fibers. These crystal-bearing fibers consist of rows of rec- 
tangular, thin-walled cells, each cell bearing, as a rule, a single crystal. 
The cells surround the bast fibers or bast bundles. They are very 
abundant and distinct in the bark of Salix, Quercus, and Populus, for 
example. They enclose completely the single enormous bast cells of 
quebracho, and occur in the majority of bast-bearing barks and stems, 
and are associated with the bast tissue of vascular bundles. Bast cells 
are essentially non-elastic ; the crystal-bearing cells and fibers enclosing 
the bast give elasticity. This is shown to a remarkable degree in 
the inner bark of Quillaja, which contains an enormous quantity of 
large, elongated prismatic crystals of calcium oxalate distributed 
through the bark parenchyma. 
2. In other instances the crystal-bearing cells are not merely an 
aid to mechanical tissues, but serve as a substitute therefor, function- 
ally taking the place of sclerenchyma. For example, in the seed of 
quince there is found a sclerenchymatous tissue below the layer of 
mucilaginous epidermal cells. In the white garden bean this scleren- 
chymatous tissue is replaced by a layer of cells carrying large prismatic 
