August i, 1908.] 



THE INDIA RUBBER WORLD 



365 



The Anatomical Structure of Guayule. 



/)'_v Alfred Dominikus, Diisscldorf. 



DURING a sojourn in Mexico, Dr. H. Ross, the custodian 

 of the botanical museum at Munich, investigated the phy- 

 totomy* of the guayule plant {Parthcnium argcntatum, 

 A. Gray), after having previously used the dried specimens in the 

 'botanical collection at Munich for preliminary investigations. 

 The results of the researclies made by tliis learned naturalist, as 

 published in the Berichie der Dcutschcn Botanischen Gesellschaft 

 (Reports of the German Botanical Society), with instructive il- 

 lustrations, are well deserving of commendation. 



The features which appear of foremost interest to us are 

 firstly, the secretion, and, secondly, the cells of the parenchyma 

 (the fundamental cellular tissues), inasmuch as the latter con- 

 tain the rubber substance. 



The secretion vessels may be divided into primary and sec- 

 ondary. The primary resin ducts, which are developed in the 

 immediate vicinity of the points of growth, are formed by schizo- 

 genesis — /. c, by fission of the cell rows. They are found in the 

 sprout axis, in the primary bark, and in the pith, and appear to 

 be closely connected with the vascular bundles, as regards their 

 distribution. Their number ranges between 12 and 25. Their 

 cross section is at first approximately circular, but will finally 

 show a perceptible elongation in a tangential direction. In stalks 

 of 2 to 3 millimeters diameter, the average measurements of 

 these ducts are o.i X 0.3 millimeter. They are less numerous in 

 the pith, in which they retain their circular cross section through- 

 out, until they disappear with the withering of the pith. The 

 upper and under sides of the thick nerves or veins of the leaves 

 and leaf stems are each provided with one secretion vessel, while 

 the thin veins or nerves are generally devoid of secretion vessels, 

 or else only one is found on the side of the "wood part." The 

 primary root bark contains a few ducts, whose cross section is 

 usually greatly elongated. 



The secondary resin ducts, which are likewise formed by 

 schizogenesi'S, originate in the layers of the leptome (bast), en- 

 closed by delicate walls. Since they never extend to the paren- 

 chyma strips, and are, consequently, enclosed between the same, 

 they are generally smaller in width, but never wider than the 

 adjacent parts of the leptome. Their further development in the 

 inner bark is repeated, separately for each zone or belt and at 

 regular intervals, according to the growth of the plant in thick- 

 ness. Usually only a small strip of leptome remains wholly intact 

 at each new development, inasmuch as its place is taken up by the 

 secondary secretion ducts. The latter are divided by the newly 

 formed parenchyma strips, their cross section thus, of course, be- 

 coming continually shorter (0.04 to 0.05 millimeter), which makes 

 them all the more numerous. The cells which line the resin ducts 

 abound in protoplasm, and they may be discovered in advance, 

 since zinc chlorid-iodine gives a yellowish color to their contents, 

 while the same reagent colors the cells of the surrounding tissues 

 blue, inasmuch as they contain starch. 



The secretion from the cells which surround the ducts is in 

 the form of an essential oil which, however, soon becomes re- 

 sinous and appears in the form of colorless or slightly yellowish 

 drops or aggregations. It is wholly soluble in alcohol, ether, 

 chloroform, toluol, and xylol. Alcannin will color it red, and 

 zinc chlorid-iodine. iodine or a mixture of iodine and sulphuric 

 acid will impart a light yellowish color to the substance. 



The substance which supplies the rubber is contained in the 

 pith, in the strips of parenchyma, the wood parenchyma, and the 

 primary bark, and consequently in nearly all the cells of the 

 fundamental tissue. Ross observed the following reactions : One 

 per cent, osmic acid imparts a dark brown or black color to the 



•Vegetable anatomy. 



contents of the ceils in question. Zinc chlorid-iodine colors them 

 light brown, while alcannin makes them intensely red. They are 

 not soluble either in cold or boiling alcohol, in ether or in chloro- 

 form, even if they are left for hours immersed in either of the 

 said fluids. They do not disappear from the cells, if treated with 

 concentrated potassium lye, either hot or boiling, not even if 

 they are subsequently boiled in alcohol. A mixture of chloral 

 hydrate (5 parts) and water (2 parts) produces a very consider- 

 able change in the contents of the cells, causing a part of the 

 same to disappear. When immersed in a mixture of potassium 

 lye and alcohol, the contents will form spherical masses inside 

 and outside the cells. The beautiful wine red color imparted to 

 the contents of the cells by treatment with a concentrated solu- 

 tion of sugar in sulphuric acid, indicates the presence of al- 

 buminous compounds. 



The bark contains a considerably larger amount of rubber than 

 the wood itself, the only parts of the latter containing rubber 

 being the parenchyma strips and the only slightly developed wood 

 parenchyma. In consequence of the withering of the pith and of 

 its resin ducts, the rubber obtained from comparatively old w-ood 

 contains, however, considerably less resin. The wood parts of 

 the root would presumably supply a product entirely free from 

 resin. The leaves contain either only small amounts of sub- 

 stances resembling rubber, or none at all. Only a small amount 

 of rubber is accumulated in comparatively young plants, and the 

 amount increases only very gradually. It would, therefore, not 

 pay to utilize the plants before they are ten years old. 



Similar plants investigated by Dr. Rr.ss were the Parthciiium 

 tomciitosuiii. D. C, and Parlltciiitiiii iiicanum, H. B. K., the secre- 

 tion ducts of which, containing resin, resemble those of the 

 Parthcniuni argcntatum in both structure and arrangement. The 

 bark and parenchyma strips of the oldest part of a blossoming 

 branch were found to contain a considerable amount of sub- 

 stances whose micrcchemical reaction was similar to that of the 

 rubber substances contained in the guayule. 



THE LARGE PRODUCTION OF GUAYULE. 



IX reporting on the condition of the guayule rubber trade, the 

 Mexican Herald of recent date said : "At present the prices 

 of guayule have suflfered in common with other products, but the 

 fartories are working incessantly in the production of the gum, 

 which finds a good market in the United States for such quanti- 

 ties as may be produced in Mexico under the present facilities. 

 There are many guayule factories and all are said to be working 

 up to the limit." 



The same article says that practically four-fifths of the whole 

 guayule production goes to the United States and the remainder 

 to Europe, mainly to Germany. It is suggested that the German 

 manufacterers are showing an increased interest in this material, 

 and that should they become more liberal buyers it may have 

 the effect of sending up prices. 



The Herald's statements are borne out by the statistics of 

 Mexican exports. Whereas the total exports of rubber from 

 that country during the ten years 1889 to 1898 inclusive averaged 

 less than 200.000 pounds a year, they amounted during the fiscal 

 year ended June 30, 1907, to 10,321.247 pounds, and for the first 

 ten months of the last fiscal year to a still larger total — 

 10.106. 100 pounds. In other words, the increase has been from 

 about 88 tons a year to the rate of 5500 tons a year. And the 

 increase has been due chiefly to the development of guayule 

 rubber. 



The comparative statement which follows, of the imports of 

 Mexican rubber bv the United States and Germany for the first 



