Gums, Resins, 



108 



[Feb. 1908. 



the central area may be said to be stocked 

 with Guayule, yielding: on the average 

 half ton per hectare (J ton per acre). 

 The total supply of Guayule available is 

 estimated at from 400,000 to 500.000 tons, 

 but Mr. Hexly C Pearson, the American 

 expert of the " Indian Rubber World" 

 (New York), allows only 800,000 tons. 

 Investigations into the yield of rubber 

 made by a competent chemist at Jimulco 

 gave a result of 7-12 per cent, which 

 agrees well with Pearson's figures of 6-11 

 per cent. Dr. Endlieh, quoting from 

 Pearson (in "El Financiero Mexicano," 

 15 de Averil de 1907) states that the ex- 

 port of Guayule rubber up to the end of 

 January, 1907, was 0,100,000 lbs., of which 

 2,700.000 lbs. go to the second half of 1906 

 and 700,000 to January of the current 

 year. The last prices quoted were 65 

 cents erold per lb. per New York, and 

 5'50— 5'75 M. per Kg. per Hamburg. The 

 extent to which Guayule land is restocked 

 spontaneously is satisfactory, as there 

 are plenty of seeds and the seeds germiu- 

 ate readily; but growth is slow, ten 

 years being about the time required for 

 a Guayule plant to become fit for a pro- 

 fitable working. By that time the stem 

 should have a diameter of § in. at the 

 base. As to cultivating the plant Dr. 

 Endlieh is more hopeful now. Although 

 the experiments made in that direction 

 were on a small scale, he considers the 

 fitness of the Guayule for plantation 

 proved. Wherever soil and climate cor- 

 respond to the physical conditions pre- 

 vailing in the Mexican Guayule region, 

 waste land may be profitably stocked 

 with Guayule, particularly along with 

 cattle-rearing as the primary iudustry. 

 So far as soil is concerned the presence 

 of a certain amount of lime seems to be 

 essential, and as to climate it should be 

 kept in mind that the occurrence of the 

 Guayule shrub in the central area is 

 limited to altitudes between 900 to 

 1,700 m. Sloping or uudulating ground 

 would answer best the situations of its 

 natural habitats. Owing to the fact 

 that Mariola (Partheniiuiv incanum) has 

 been mistaken for the Guayule (P. argen- 

 tatum), it seems desirable to provide, if 

 possible, against a repetition of the mis- 

 take. The following diagnostic com- 

 parison of the two plants, prepared by 



Dr. O. Stapf may, it is hoped, serve this 

 purpose. Although the structure of the 

 flowers and flowerheads of Partheniuta 

 argpntntum, A Gray, and P. incanum, 

 H. B. K., is very similar, there ought to 

 be no difficulty in distinguishing the 

 two plants, particularly when they 

 grow, as is frequently the case, side by 

 side. To facilitate comparison the more 

 salient characters are set out here in 

 parallel columns. 



Parthenium Argen- 

 tatum. 



A small shrub with a 

 short stem and very 

 numerous, much di- 

 vided branches, from 

 less than 1 and over 

 3 ft. high ; woody per- 

 sistent branches short, 

 more or less g arled, 

 covered with a rather 

 smooth, dark grey bark; 

 young shoots silvery 

 grey all over. 



Leaven lanceolate, 

 acute, entire or more 

 often with 1-3 coarse 

 acute teeth or lobes, 

 1-2 in. long, 2-6 in. 

 wide, densely covered 

 with a fine silvery grey 

 tomentum, gradually 

 narrowed into an often 

 long and slender peti- 

 ole. 



Flower heads subses- 

 sile, subglobose, 2-1 in. 

 in diameter, 3-7 in a 

 cluster; clusters at the 

 ends of 2 or 3, rarely 

 more, slender branches, 

 collected into a very 

 imperfect corymb, rare- 

 ly solitary. 



Involucre silky pube- 

 scent outer bracts 

 broadly herbaceous on 

 the back. 



Parthenium inca- 

 num. 



A small shrub, 1-2 ft. 

 high, much branched ; 

 woody persistent 

 branches, elongate, 

 slender, covered with a 

 somewhat rough bark, 

 cracking longitudinal- 

 ly; young shoots finely 

 whitish or greyish 

 wooly. 



Leaves obovate to ob- 

 ovate-oblong in outline, 

 crenate (the smaller) 

 to deeply pinnatilobed 

 ^-1 in. long (rarely 

 more), £-§ in. wide, 

 lobes 1-2 in. on each 

 side, entire or the ter- 

 minal crenate, all very 

 obtuse, the whole leaf 

 densely covered with a 

 white wooly tomentum 

 when young, then grey- 

 ish ; petiole very short. 



Flower heads pedun- 

 cled, or subsessile, 2-1 

 in. in diameter, in 

 terminal, often much 

 branched corymbs, 1-4 

 in. in diameter, bran- 

 ches slender. 



Involucre finely vil- 

 lous; outer bracts 

 slightly herbaceous on 

 the back above the 

 middle. 



Specimens of the Guayule plant (P. 

 argentatum) and of Mariola (P incanum) 

 presented by the Foreign Office, also a 

 sample of Guayule rubber, presented by 

 the Compania Explotadora Coahuilense, 

 are exhibited at Kew in Case 68, Museum 

 No. 1.— Royal Botanic Gardens, Kew, 

 Bulletin, No. 7, 1907. 



