26 



RUBBER-CONTENT OF NORTH AMERICAN PLANTS. 



hoped to reduce the error due to individual variation, although it is 

 admitted that a much larger niunber would give more convincing data. 

 The results as shown in table 3 imder Nos. 1034 and 1035 indicate 

 that mature leaves contain the highest percentage. This is in accord- 

 ance with the analyses reported under Nos. 826 and 827, where younger 

 and older leaves from individual plants are compared, and with what 

 has been suggested from other species. No. 1036 seems, however, to 

 be an exception, perhaps accoimted for by the pathologic conditions 

 of the foliage. 



Another item of interest brought out in table 3 is the fact that largs, 

 robust plants, like No. 1032, may carry as high or higher percentages 

 of rubber in their leaves as average or small ones, 'fhe practical 

 application of this is self-evident. In common with the other species 

 examined, excepting only A. subulata, the amount of rubber in the 

 stems is almost negligible. 



Table 3. — Chemical analyses of Asclepias syriaca. 



No. 



Place of coUection. 



Date of 

 collection 



Part of plant 

 analyzed. 



Acetone 

 extract. 



Rubber 

 (benzene 

 extract). 



826 



827 



806 

 898 

 1032 

 1034 

 103S 

 1036 



Madison, Nebr. 



Aug. 27 



.do. 



.do.... 



Near Humphrey, Nebr. •. 



Enola, Nebr 



Lincoln, Nebr. * 



do 



do 



do 



Sept. 25 

 Sept. 24 

 Oct. 20 

 ..do.... 

 ..do.... 

 ..do..., 



Leaves ' 

 Leaves ' 

 Stems ' . 

 Stems * . 

 Leaves ' 

 Leaves * 

 Stems*. 

 Leaves . 

 Stems . . 

 Stems. . 

 Leaves . 

 Leaves . 

 Stems.. 

 Leaves' 

 Stems . . 

 Leaves" 

 Stems . . 

 Leaves ' 

 Stems.. 



ct. 



8.8 



11.6 

 6.5 

 9.8 



10.6 

 5.5 



10.2 

 6.4 



11.8 

 4.4 

 8.6 

 5.7 



p. ct. 

 1.4 

 2.4 

 0.3 

 0.21 

 0.53 

 1.10 

 0.27 

 4.2 

 0.2 

 0.4 

 2.1 

 4.1 

 0.3 

 3.6 

 0.3 

 4.4 

 0.4 

 3.3 

 0.6 



> Young. 



' Old leaves from lower down. 



• Upper portion. 



* Lower portion. 



' Between Humphrey and Madison. 



• Very large plant; leaves just turning yellow. 

 ' Dried while green; mixture from 5 plants. 



• Dried when yellow; mixture from 5 plants. 



• Dried when yellowing; mixt\ue from 5 plants, 

 partly mildewed. 



Asclepias californica. 

 Synonym: Gomphocarpits tomentosus. 



Description. — Plant a rounded perennial herb, 2 to 3 feet high and 

 about as broad; roots exceptionally large, branching near the surface 

 of the soil to form a broad crown; stems usually 4 to 10, unbranched, 



