August 1, 1913., 



THE INDIA RUBBER WORLD 



565 



METHOD OF SECRETION. 



The first evidence of secretion is seen in the occurrence of very 

 minute granules in the protoplasm. With the increase in their 

 number and size they migrate into the sap-vacuole, and can be 

 seen there by their Brownian movements. The analogy of this 

 condition with that in the latex vessels of latex rubl)er plants is 

 obvious, and indeed there may be more than mere analogy. In 

 the definitive condition the rubber takes the form of a large drop- 

 let, almost lining the sap-vacuole, and rendered heterogeneous in 

 its internal structure by the inclusion of encystments of solutions 

 containing, probably, albuminous, carbohydrate and hydrocarbon 



I Wii SllASd.Ns' (iRdWTH FROM .StchIv L'nDKR 1 RRICATKIX , /,Ai:ATKr.\ S, 



sul)stances. It is important to note here that the rupture of the 

 wall separating two adjoining cells would be followed liy the 

 contact and merging of the two contained rublter droplets. This 

 is the more sure residt, the larger the droplets, and this explains 

 the ready agglomeration of guayule rubber into "worm rubber" 

 in the pebble mill when field plants rich in rubber are used. 

 Conversely, the smaller the droplets, the more increasingly diffi- 

 cult is the same result, calling for special methods of treatment. 

 The droplets can be so small as to be impossible of mechanical ex- 

 traction in the usual sense ; this happens when they arc so small 

 as to form a suspension. The agglomeration of the suspensoids 

 might be possible by the use of a minimum of water and the 

 action of a "coagulating" agent, involving technical difficulties. 

 the overcoming of which would be of the highest interest, but 

 probably not economically of importance in this special case. 



The largest rubber content under irrigation with known con- 

 ditions was attained by plants of two seasons' growth in Zacatecas. 

 At the close of the second season's grow-th the rul>ber content ap- 

 peared as in the first stage of development, namely as minute 

 droplets or granules. Seven months later, after practically' con- 

 tinuous drought, the amount of rubber in the cell was less than 

 the maximum, but not by more than. say. one-fifth. It occurred 

 as a continuous mass, almost identical in appearance with the 

 normal. In this case, the small percentage of rubber, on dry 

 weight, is due in very large part to the great development of tis- 

 sues which do not contain rubber in appreciable tpiantities. The 

 use of abundant water in irrigation cannot be said to have inhib- 

 ited the secretion of rubber, but rather to liave increased the 

 growth of barren tissues. 



The problem from the economic viewpoint is, therefore, in such 

 case not the possibility of extraction so much as the increased 

 cost of handling a much greater volume of bagasse, though it 

 is probable that this in itself would lend some hindrance to ex- 

 traction. 



The material grown at Tucson from stocks showed its rubber 

 cells to contain a dense emulsion-like mass, filling the sap cavity 

 in August of the third season's growth. In the previous August 

 the same cells showed only minute granules. Seedlings in Aug- 

 ust of their second seasons contained in each cell an irregular 

 solid mass of rubber occupying one-tenth to one-eighth of the 

 sap-cavity, accompanied by (piite small droplets elsewhere. As 

 the irrigation had not been controlled or definitely applied and 

 suspended, it is probable that the conditions had not been the 

 best possible for the secretion of rubber. 



Practically the same result was obtained for plants grown from 

 stocks at Auburn when examined early in September (1912) in 

 their third season. If we compare these cases from Alabama and 

 fiom .Xrizona with the mariola (Parthenium incanum) we find 

 but little difference between them, either as regards the amount 

 of ruliber in the cells or its character. 



Two Sea.sons' Growth at Auburn (Ala.) from Texas Stock. 



The conclusion is inevitable, I believe, that the determining 

 factor in the cultivation of the guayule is: control of the water 

 supply. In the presence of an abundance of water applied ir- 

 regularly and at too frequent intervals, it will require more than 

 three years for the majcimum cell content of rubber to be at- 

 tained. A quantum approaching the maximum is reached, on 

 the other hand, if plants which have been well irrigated for two 

 seasons are then subjected to drought conditions for six to eight 

 months. That merely rate of growth is not correlated with the 

 secretion of rubber is shown by the condition found in a plant 

 grown from seed in a 12-inch pot in limestone soil for two years, 

 and planted out for a season (summer of 1912) at Auburn. These 

 plants were in some cases at a standstill for a year previous to 

 planting out, and for various reasons grew but little in the open. 



