46 RUBBER-CONTENT OF NORTH AMERICAN PLANTS. 



VIII. SPECIES EXAMINED WITH NEGATIVE RESULTS. 



In the attempt to discover as many rubber-bearing species as possible 

 many sorts were examined on the mere chance that rubber might be 

 present. In a few cases it was unexpectedly found in non-latex 

 plants, as indicated in the preceding table. The remaining species, 

 those in which no rubber could be detected with certainty, are enum- 

 erated below. All were subjected to a chemical analysis, but in no 

 case was more than a fraction of 1 per cent of benzene extract obtained. 

 Such small amounts are almost certainly some other substance than 

 rubber when they occur in non-latex plants. The locality mentioned 

 for each species is the place of collection of the sample. 



A. CompositjE. 



876. Achillsea millefolium, Pike's Peak, Colorado. 

 393; Ambrosia artemisiifolia, Manitou, Colorado. 



395. Ambrosia trifida, Manitou, Colorado. 



873. Anaphalis margaritacea, Mount Manitou, Colorado. 



396. Artemisia campestris, Manitou, Colorado. 



877. Aster bigelowi. Pike's Peak, Colorado. 



865. Bahia dissecta, Manitou, Colorado. 



1107. Baileya multiradiata, Santa Rita Reserve, Arizona. 

 906. Balsamorhiza deltoidea, near La Grande, Oregon. 



1040. Balsamorhiza deltoidea, Ogden, Utah. 

 904. Bidens frondosa. Twin Falls, Idaho. 



878. Brickellia wrighti, Canyon City, Colorado. 



908. Chrysanthemum balsamita. Grant's Pass, Oregon. 



868. Chrysopsis villosa, Manitou, Colorado. 



946. Chrysothamnus howardi, Buena Vista, Colorado. 



809. Dysodia papposa. Northern Texas. 

 1104. Encelia farinosa, Tucson, Arizona. 



326. Eriophyllum lanatum integrifolium. Eastern Colorado. 

 875. Gaillardia aristata. Royal Gorge, Colorado. 



819. Gutierrezia texana, Texas. 



867. Gymnolomia multiflora, Manitou, Colorado. 



883. Haplopappus parryi. Pike's Peak, Colorado. 



864. Haplopappus spinulosus, Colorado Springs, Colorado. 



929. HeUanthus ciliarus, near El Paso, Texas. 



948. Hymenopappus filifolius, Buena Vista, Colorado. 



392. Iva xanthifolia, Manitou, Colorado. 



866. Kuhnia eupatorioides, Manitou, Colorado. 

 862. Liatris punctata, Colorado Springs, Colorado. 



852. Parthenium incanum, San Andreas Mountains, New Mexico. 



850. Pectis angustifolia, Sonora, Texas. 



810. Pectis papposa, Western Texas. 



901. Pericome caudata, Pike's Peak, Colorado. 



1108. Psilostrophe cooperi, Tucson, Arizona.' 

 830. Senecio Slifolius, Western Texas. 



903. Solidago occidentalis. Twin Falls, Idaho. 



861. Thelesperma trifida, Colorado Springs, Colorado. 



874. Verbesina dissecta, Manitou, Colorado. 



820. Vernonia marginata. Northern Texas. 



851. Zinnia grandiflora. Las Cruces, New Mexico. 



' A sample of Psilostrophe cooperi from Las Cruces, New Mexico (No. 805, September, 1919) 

 yielded 1.4 per cent of benzene extract, indicating that rubber is possibly present in this species. 



