116 THE AMERICAN BOTANIST. 



not found in the immediately surrounding district. These 

 are the skunk-cabl3age {Svmplocarpos /cet/ius), for which 

 this is the only station in the county, and which is not 

 found again for about four miles to the south when it 

 becomes common; th^ northern bedstraw (Galium bore- 

 ale) which is not found for six miles to the south, and for 

 at least twenty miles north, and eighteen miles east; the 

 horse gentian (Triosteum perfoliatum) which is absent 

 from the surrounding three miles of territory ; and the 

 early golden-rod {Solidago juncea) which is not met. 

 with again for a mile south, and at least ten miles north, 

 and four miles east. The conclusion to which we are 

 forced is that there is some influence tmfavorable to these 

 species on the surrounding mainland but absent from the 

 island. — A. B. Klugh, Geu/ph, Ontario. 



Sources of Rubber. — Four families, all of them hav- 

 ing representatives in the North Temperate Zone, turnish 

 the rubber of commerce. The Apocynaceee is familiar 

 through the dog-banes (Apocyniim) the Asclepiadaceas by 

 the milk-weeds (Asclepias) the Euphorbiaccce by the spur- 

 ges (Euphorbia) and the Urticaceas by the nettles ( Urtica). 

 The great majority of the plants belonging to these fam- 

 ilies have a milky juice similar to that from which rubber 

 is made but only a few genera furnish species that are 

 commercially^ valuable. The Euphorbiaceae probably 

 stand first on the list with the genus Hevea which yields 

 Para rubber and Manihot the source of Ceara rubber. 

 Both of these are American genera. The rubber producers 

 of the Urticaceas are found chiefly among the figs (Ficus) 

 and the bread-fruits (Artocarpus). The Apocynaceae have 

 an unusual number of genera with rubber yielding species. 

 No less than eight or ten are known to commerce and the 

 number of species is much greater. They are found mostly 

 in the Old World. The Asclepiadaccfe are of least impor- 

 tance, the principal rubber producer being Cryptostegia 

 grandiflora. Doubtless there are many other plants with 

 a milky juice that would yield a good grade of rubber, but 

 the expense of extraction prohibits their use. 



