294 



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 argentatum. 



A small shrub with a short stem and 

 very numerous, much divided branches, 

 from less than 1 to over 3 feet high ; 

 woody persistent branches short, more 

 or less gnarled, covered with a rather 

 smooth, dark grey bark ; young shoots 

 silvery grey a)l over. 



Leaves lanceolate, acute, entire or 

 more often with 1-3 coarse acute teeth 

 or lobes, 1-2 in. long, 2-6 lin. wide, 

 densely covered with a fine, silvery 

 grey tomentum. gradually narrowed 

 into an often long and slender petiole. 



Flower /wads subsessile, subglobose. 

 2 lin. in diam., 3-7 in a cluster ; clusters 

 at the ends of 2 or 3, rarely more, 

 slender branches, collected into a very 

 imperfect corymb, rarely solitary. 



Involucre silky pubescent; outer 

 bracts broadly herbaceous on the back. 



Parthenium incanum. 



A small shrub, 1-2 feet high, much 

 branched ; woody persistent branches, 

 elongate, slender, covered with a some- 

 what rough bark, cracking longitudi- 

 nally ; young shoots finely whitish or 

 greyish woolly. 



Leaves obovate to obovate-oblong in 

 outline, crenate (the smaller) to deeply 

 pinnatilobed, £-1 in. long (rarely more), 

 J-f lin. wide, lobes 1-2 on each side, 

 entire or the terminal crenate, all very 

 obtuse, the whole leaf densely covered 

 with a white woolly tomentum when 

 young, then greyish ; petiole very 

 short. 



Flower heads shortly peduncled, or 

 subsessile, 2 lin. in diam., in terminal, 

 often much branched corymbs, 1-4 in. 

 in diam. ; branches slender. 



Involucre finely villous ; outer bracts 

 slightly herbaceous on the back above 

 the middle. 



Specimens of the Guayule plant (P. argentatum) and of Mariola 

 (t.tncamtm), presented by the Foreign Office, also a sample of 

 iTuayule rubber, presented by the Compania Explotadora Coahuil- 

 ense, are exhibited at Kew in Oase 68, Museum No. I. 



XLVIL-A NEW RUBBER TREE : PALO AMARILLO. 



ft 



) 



Stapf ; syn. E. elastica, Altamirano and 



Otto Stapp. 



In July 1900, Dr. Altamirano, Director of the Instituto Medico 



ttSi *I eX1C0 ' and Dr - J - N - Rose > Assistant Curator of the 

 HW n r M # use " m ' WashiQ gt<>n, published a description and 

 £ f* tlons ° f a new species of Euphorbia (E. elastica) known in 

 thtZ* ^ Pal( \ Am *rillo. From the name, a footnote, and 

 ™ ,?? ° f the plates ' U could be gathered that the plant 

 fXr ™« ^ reco 1 miIiended for the Production of rubber. A 

 tuner memoxr on the subject by Dr. Altamiranof appeared in the 



^ 



Rose^p nov W ^Tl^i T P * lo Q Amar "lo (Euphorbia elastica, Altamirano and 



memoriamtiSo^TmnVfl Pa *° A^ rill ° como P™ductor de caucho. Primera 

 seen. * C ° " lm P renfca ? fototipia de la Secretaria deFomento, 1905).-Not 



