38 RUBBER-CONTENT OF NORTH AMERICAN PLANTS. 



of long, silky down and are therefore carried considerable distances by 

 wind and water, and also by creeping rootstocks. When these root- 

 stocks are divided, as in plowing, each piece gives rise to a new plant. 

 The proper place for experimental plantings would be in moist sandy 

 soil unsuited to agricultural crops. The other species of Apocynum 

 here considered, that is, A. androscemifolium, is a usually smaller plant 

 with more spreading branches and grows in drier soils. Nothing has 

 been thus far discovered that brings it into the list of promising plants 

 for rubber culture. 



Rubber-content. The Indian hemp is considered as one of the 

 most promising plants for further investigation. It is true that most 

 of the analyses indicate only small percentages of rubber, but the high 

 yield of No. 1039, together with the ease of vegetative propagation in 

 poor, sandy soils and the high quality of the product greatly modifies 

 our opinion of its possibilities. It is not unlikely that further search 

 will discover still better plants, and any strain which may be developed 

 through breeding can be perpetuated through the use of rootstocks. 

 The foliage is too sparse and thin to yield much tonnage, but this is 

 somewhat compensated by the large size to which the plants grow 

 and the density of the stand under favorable conditions. 



The first studies of the latex of Apocynum were by Fox (1912). He 

 worked especially with A. androscemifolium, but this and the larger 

 A. cannabinum, or true Indian hemp, are so much alike in other 

 respects that the latex and rubber of the two are doubtless quite 

 similar. According to this investigator, the latex is coagulated neither 

 by acids nor by alkalies, but it coagulates slowly and slightly on boiling, 

 and immediately and completely by the addition of acetone in the 

 proportion of 1 : 10 by volume. He reports further that formaldehyde 

 coagulates it readily but much more slowly than acetone, and that the 

 latex is coagulated by phenol, this giving a soft product. Fox also 

 tried a salt solution and found that this coagulated the latex slowly, 

 giving a finely divided precipitate hard to coalesce. Boiling the salt 

 solution gave a soft product. Of all the methods tried, the use of 

 acetone, perhaps with formaldehyde, was the one especially recom- 

 mended as giving the best results. The condition of the soil in which 

 the plants are grown exerts an influence upon the amount and quality 

 of the rubber in the latex, according to Fox. He found that plants 

 grown upon dry, sandy soil at West Akron, Ohio, gave a latex contain- 

 ing 2.27 per cent of rubber and 20.69 per cent of resin, whereas plants 

 grown in the swamps of South Akron contained 1.12 per cent of rubber 

 and 15.04 per cent of resin; also that rubber from dry-grown plants is 

 of better quality than that of wet-grown plants. Because of more 

 recent discoveries as to the great extent of individual variation in 

 these and similar plants, such conclusions need verification by a long 

 series of examinations before they can be accepted as final. 



