46 



GROWTH OF PLANTS 



The most thorough study in inducing dormancy m seeds is that of 

 W. E. Davis "• ^o on seeds of Ambrosia trifida and XantUum. This was a 

 joint contribution of this Institute and the Department of Botany and 

 Plant Pathology of Kansas State Agricultural College. Ambrosia seeds 



Figure 13. Germination of embryos of Ambrosia trifida taken from fruits that had 

 been stored for three months as follows: A, dry; B, in a germinator m a refrigerator; 

 and C, in a germinator at 27° to 30° C (80° to 86° F). 



consist of an embryo covered with a paper-thin transparent seed coat. 

 The seed is enclosed in a thick, woody, indehiscent fruit coat (Fig. 12). 

 In controllmg germination and dormancy the seed coat and not the fruit 

 coat is important. Ambrosia seeds (embryos) are dormant and they after- 

 ripen slowly and incompletely after several months of dry storage and 



