INTRODUCTORY 13 



a depth of thirty-six inches. The buried weed seeds showed 

 a decided loss of vitality when compared with the control samples 

 that were kept in storage. The latter germinated fifty-three 

 per cent, on the average; those buried to a depth of six inches 

 germinated twenty per cent. ; eighteen inches, twenty-six per 

 cent. ; and thirty-six inches, thirty-one per cent. 



Ewart, of the University of Melbourne, Australia, made 

 exhaustive vitality tests of six hundred different species of 

 seeds taken from a collection that had been compiled and stored 

 in a dry, airy and dark cupboard by Prof. McCoy in 1856, and a 

 large number of specimens of seeds, of varying ages, from the 

 national herbarium and other reliable sources. In his deductions 

 from the results of over 3,000 tests, Ewart gives a list of those 

 relatively few species that may be expected, under favourable 

 conditions, to retain their vitality beyond fifteen years, nearly 

 all of which species are included in the following botanical 

 families: Leguminosae, Malvaceae, Myrtaceae, Nymphaeaceae, Labi- 

 atae and Irideae. Forty-eight specimens of seeds of the genus 

 Brassica (the Mustard family) were tested. The fresh seeds 

 gave a germination as high as eighty-six per cent, and one lot 

 twelve years old gave a germination of thirty per cent. None 

 of the Brassica samples fifteen years old or more germinated, 

 although six of them were less than twenty years old. 



CONTROL AND EXTERMINATION OF WEEDS. 



In adopting a method of extermination, the nature of the 

 plant and its habits of growth must first of all be considered. 

 Some experience is necessary to know the best time to work 

 certain soils or to deal with special weeds, as well as to recog- 

 nize them in all their stages. Some weeds, Russian Thistle and 

 Stinkweed, for instance, have a very different appearance when 

 young and when mature. No general rule can be given, as the 

 treatment must vary with different districts, different soils, 

 and different climatic conditions. What may be successful in 

 one place may fail in another. 



