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JxiiibUb INTRODUCTION 



In 1942 and 1943 the Botany and Plant Pathology Division, Canada Depart- 

 ment of Agriculture, undertook a general survey of native and introduced 

 plants thought to be capable of yielding natural rubber. Wide publicity was 

 responsible for an excellent response to the request for plant material and 

 in 1942 over 1400 samples were collected fron all paz^s of Canada* Species 

 of certain generic groups including Apocynum, Asclepias, and Solidago, es- 

 tablished in plots at Ottava, provided an additional 400 samples in 1943 • 

 The present publication presents the results of analyses of rubber and resin 

 contents of this plant material* 



MATERIALS AND METHODS 



On receipt of the plant material it was, vAiere possible, divided into 

 roots, stems, and leaves and if not already in a dry condition it was dried 

 at 65°C in a forced draft oven* To ensure proper identification a specimen 

 prepared from each collection was deposited in the herbarium of the Botai^y 

 and Plant Pathology Division at Ottawa* The dried samples were ground in 

 a laboratory hammer mill and stored in cardboard containers for analysis* 



The extraction method of Hall and Goodspeed (2) has frequently been 

 used for the determination of the rubber content of plants* This method 

 involves extraction in two steps: first, with acetone to remove resins, 

 fats, coloring matters etc*; then with benzene to remove the rubber* As a 

 considerable number of materials are soluble in benzene as well as acetone, 

 the reliability of this extraction method depends on the completeness with 

 v^ch the nonrubber benzene-soluble constituents are removed in the first 

 extraction* Hall and Goodspeed (2) used extraction periods of three hours 

 but other workers (1,3 j4, 5) have used periods of from six to sixteen hours* 

 Longer extraction periods increase the accuracy of the determination but 



