199 



New Rubber-containing Plants.— Rubber (including gutta-percha) 



is known to occur in about a dozen familes of plants, of which 

 the more important are the Euphorbiaceae, Urticaceae (Moraceae), 

 Apocynaceae, Asclepiadaceae and Sapotaceae, whilst the Loran- 

 thaceae and Compositae will probably also become of considerable 

 importance in the near future (see Tropenpflanzer, 1905, p. 633 ; 

 and Kew Bull, 1906, p. 218 ; 1907, p. 285). In the remaining five 

 families the occurrence of rubber is at present a matter of 

 theoretical interest only, as it has not yet been shown that its 

 extraction would be remunerative ; they are the Trochodendraceae 



{Eucommia\ Tiliaceae {Plagiopterori), Celastraceae, Hippo- 

 crateaceae and Lobeliaceae {Siphocampylus), whilst a sixth, 

 Convolvulaceae, is given by Czapek as also containing rubber 

 (Biochemie, vol. ii, p. 709). 



The presence of rubber in three African species of Gym- 

 nosporia (Celastraceae) is recorded in the Notizblatt des Konigl. 

 botanischen Gartens imd Museums zu Berlin, No. 42 (Bd. V.), 

 of March 11th, 1908, by Dr. Th. Loesener, who prefaces his 

 account by a summary of our knowledge of the occurrence of 

 rubber in the family. 



Radlkofer, who was the first to detect rubber in the Celastraceae, 

 found it in the Mexican genus Wimmeria {Bot. Gaz. vol. xviii., 

 1893, p : 199). The leaf anatomy of the Celastraceae was after- 

 wards investigated with special reference to the occurrence of 

 rubber by Metz, who recorded its presence in special laticiferous 

 cells of the leaves in eight species of Wimmeria and in the South 

 African Mystroxylon eucleaeforme, whilst in no fewer than 

 thirteen genera, rubber was present in the form of small masses 

 in the cells of the parenchyma (Beih. Bot. Centralbl. vol. xv M 

 p. 309) ; in some of these genera however, the rubber may have 

 been present in laticiferous cells in the stem and root, although 

 not occurring in special cells in the leaves ; this was found to be 

 the case in Eiwnymus, for example, by Col (Comptes Rendus, 

 vol. cxxxii , 1901, p. 1,354). 



It is obvious that the extraction of rubber could not be 

 profitably undertaken, where it is present merely in the cells of 

 the parenchyma. In the three species of Gymnosporia investi- 

 gated by Loesener, however, the rubber is present in special 

 laticiferous cells, which occur in the bark, the leaves and the 

 inflorescence, but it is still unknown whether the rubber is of 

 sufficiently good quality and present in sufficient amount to make 

 its extraction profitable. Further information is also required as 

 to the geographical distribution of the three species and their 

 mode of occurrence, before an opinion can be formed as to the 

 value of Loesener's discovery. The presence of the rubber may 

 be detected by carefully breaking in two a leaf or a piece of bark, 

 when the portions remain connected by fine elastic threads which 

 stretch from one broken surface to the other and which can be 

 drawn out for a fair distance before breaking, when they rebound 

 and curl up. 



The three species, which are closely allied to one another, are 

 all spineless and are natives of intertropical East Africa. Two of 

 them, G. amaniensis, Loes., and G. bukobin**, Loes., are new 



