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Х. On the Castilloa elastica of Cervantes, and some allied Rubber-yielding Plants. 
By Sir J. D. Нооккй, К.С.8.Г, C.B., F.R.S., F.L.S. 
(Plates XXVII. & XXVIII.) 
Read December 3rd, 1885. 
THE great importance of the India-rubber trade renders it necessary that the plants 
yielding this valuable product should be known with scientific accuracy. Of these, the 
Ule, that which yields the rubber of Mexico and Central America (Castilloa elastica), 
is the earliest described, and might hence be supposed to be well known. It is the 
purport of this communication to show that this is not so, and that probably more than 
one rubber-bearing species of that genus exists in Central America under this name. 
Attention was first called to this subject by the receipt at Kew, from Dr. Trimen, 
Director of the Ceylon Botanical Gardens, of a specimen and a drawing—with complete 
analysis of the flowers and fruit—of the plant sent out from Kew in 1876 as Castilloa 
elastica, and which drawing differed considerably from Cervantes's figure and description 
of the Ule of Mexico. The tree from which the specimens were taken and drawing 
made, was raised from one of the cuttings procured in Darien (Panama) by Mr. Cross in 
1875, and which, after being grown on at Kew, were distributed to various tropical 
Colonies, as detailed in Mr. Thiselton Dyer's account of Mr. Cross's mission and of the 
introduction into Europe of the India-rubber plant which is appended to this communi- 
cation. It will be seen from that account that Mr. Cross sent the plant under the name 
Caucho, and that the locality where he procured it, the forests of the rivers Chagres and 
_ Gatun (well-known localities for India-rubber collectors) is considerably to the south of 
the botanically ascertained stations for the Ule. In selecting these forests for the 
purpose of collecting seeds Mr. Cross was, no doubt, indebted to information obtained by 
the late Mr. Sutton Hayes of Panama, and which is attached to specimens of an Ule, 
which latter, however, he procured from the Republic of San Salvador; and for 
assuming that the Caucho is the Ule or Castilloa elastica of Cervantes, he probably 
relied on the testimony of Cavanilles, who, in a notice of the Caucho of Darien (Panama) 
in the Ann. de Hist. Nat. Madrid, ii. p. 126, regards it as the same with the Ule of 
Cervantes, whose description he quotes at full length. Unfortunately Mr. Cross sent no 
other herbarium specimens of the Caucho than some very badly preserved old leaves 
and seeds, so that, until the arrival of Dr. Trimen's materials, the means of identification 
- were wanting. 
I have next to advert to specimens of the fruits of three forms or species of Castilloa 
from the forests of Honduras, preserved in fluid, kindly procured by W. H. Langton, 
Esq., Secretary of the Belize Estate and Produce Company ; two of these are named Ule, 
and both stated to yield the Honduras rubber; the third is named Tunu, and said to yield 
a gutta-percha. І have given figures of all these in Plate XXVIII. These all differ 
SECOND SERIES.—BOTANY, VOL. II. 2K 
