34 The Ottawa Naturalist. [May 



germination test with cereals.. Aeration and drying of the soil 

 produced only a slight improvement. The average percentage 

 germination from twelve tests of oats in a good fresh compost 

 soil was 86 per cent. When the same soil was used for sub- 

 sequent germination tests, after being aerated and dried, the 

 average percentage vitality of twelve tests of the same oats 

 (100 grains of oats being used for each test) was reduced to 76 

 per cent. 



If the theory of toxic root excretions is to be accepted as 

 an explanation for this falling off in vitality, as would be shown 

 by soil test, it would seem that the poisonous excretions from 

 the first crop of oats proved to be fatal to the weaker plants 

 from the second and subsequent crops. Since the oat plants 

 had been left in the soil fourteen days only, the reduction in 

 plant food would be inconsiderable. 



If, as contended b}' supporters of the "De CandoUe theory 

 of root excretions," plants excrete from their roots substances 

 which impair growth within themselves and render the soil less 

 suitable to the growth of other plants belonging to the same 

 order or having the same requirements in respect to plant food, 

 then the necessity of crop rotation in agriculture and horti- 

 culture becomes more obvious; the reasons for the so-called 

 clover sickness in some soils, "fairy rings" of mushrooms, and 

 much in connection with plant relations in nature also becomes 

 easier of explanation. 



It was suggested that, in consideration of how plants feed, 

 it would seem reasonable to expect that these toxic root excre- 

 tions, if anv, would be more abundant with a given species on 

 some soils than on others, owing to the relation between the 

 requirements of the plant and the mineral constituents in solu- 

 tion in the soil ; also that bacterial life and the fermentation 

 induced bv it in the soil might be expected largely to overcome 

 the effects of toxic excretions from plant roots. 



A short discussion on the longevity of seeds and recent 

 work by Dr. Ewart, of Melbourne University, Australia; Dr. 

 Croker, of Chicago University, and Dr. Duval, of Washington, 

 D.C., was also taken up, and the progress results of some work 

 that is being conducted by Mr. William Bond, of the seed labora- 

 tory staff, in making periodic germination tests of weed seeds 

 that were collected in 1902, were presented. The evidence now 

 available would seem to make clear that weed seeds and other 

 seeds which are buried in the soil do not retain their vitality 

 as long as when stored in a cool, dry place. There are relatively 

 few kinds of seeds which will retain their vitality for a longer 

 period than, approximately, fifteen years. Ewart found from 

 exhaustive tests that of the species which are best able to retain 



