180 Guayule. 



treatment with that reagent, the contrast between the rubber-containing 

 cells of the cortex and the empty nearby cork-cells is very clear and striking. 

 Inasmuch as the peridermal divisions, though several times repeated in the 

 same mother-cell, finally involve a considerable depth of tissue, and as 

 the rubber can not travel from cell to cell as such, we must conclude either 

 that the rubber is translocated, which is unlikely, or that it disintegrates. 

 In support of the latter conclusion we note the following ocular evidence: 



1. When the first cork-cambium division takes place the partition 

 passes through the rubber-content, whereby the two daughter-cells each 

 receive a share (plate 31, fig. 14). From the outer cell, which becomes 

 suberized, the rubber disappears. 



2. This disappearance is gradual. The rubber may first break up 

 into droplets, which become fewer in number till, in the second series 

 of cork-cells, scarcely any evidence of its former presence remains, or it 

 may become shrunken in appearance. During this time the rubber, if it 

 still is such, reacts less characteristically to alkanet, and takes on a dirty 

 bluish tint. In one young root, however, I observed droplets of rubber 

 giving the characteristic stain, out several cells distant in the cork. The 

 explanation may be that after the death of the protoplasm the oxidizing 

 enzymes present hasten the disintegration. This may be less rapid in the 

 root, though it is difficult to say why. The mere contact with the air 

 would seem an insufficient explanation, since disintegration of the rubber 

 in cortex cut out bodily by inner periderm is very slow. 



THE DEVELOPMENT OF RUBBER IN THE CELL. 



All that we are able to do microscopically in regard to the method of 

 origin of rubber in the cell is to detect its first appearance and the subse- 

 quent accumulation, and we are therefore precisely in the position of 

 the poet who said of a matter usually regarded as far removed from the 

 realm of science, 



"Sie kommt, und sie ist da." 



We are unable to say at this point whether the origin is associated with 

 special organs as plastids or not, though my observations up to the present 

 indicate that there are no such organs. 



The relation of nuclear activity in general to secretion is well known. 

 The rubber in the palisade-cells of the leaf appears first in all cases in 

 contact with the nuclear membrane, and for this reason does not take the 

 form of spherical but of concavo-convex droplets, seen in plate 43, fig. 5. 

 Elsewhere the earliest appearance is as very minute, well-nigh invisible 

 droplets (plate 41, fig. 4), scattered in the protoplasm. They grow in 

 size and increase in numbers until the protoplasm is loaded sufficiently 

 to render it exceedingly frothy in appearance (plate 41, fig. 5). These 

 droplets may travel toward the interior of the cell and be extruded into 

 the vacuole, where they run together to form a larger droplet or a more 

 or less irregular mass. This is not homogeneous, as might be supposed, 

 but is vacuolated, sometimes so much so that it is quite alveolar in struc- 

 ture (plate 41, fig. i), sometimes less so, the vacuoles being widely scat- 



