o 
488 Report OF THE HORTICULTURAL DEPARTMENT OF THE 
too, that, somehow, different crops growing in the same soil 
may injure each other or the one the other. Two theories are 
advanced to explain these antagonisms of plants. - One is that 
plants excrete toxins; the other is that the injurious effect 
arises from the action of bacteria or from the injurious pro- 
ducts of bacteria brought about by some interaction between 
the higher plants and the micro-flora. 
Pickering, of the Woburn Farm, in accounting for the in- 
jurious effect of grass upon the apple, as we have seen,'* does 
not attribute the harm done to the competition for moisture 
and food, to a difference in temperature, to a lack of air and 
oxygen or to excessive amounts of carbon dioxid, but holds 
that it is due to some ‘* actively malignant effect on the tree, 
some action on it akin to direct poisoning.” More recently the 
same experimenter leaves the question open as to whether the 
harmful action is due to toxin from the roots of the grass or to 
some change in the activity or product of the micro-flora 
brought about by the sod. 
Beside this specific experiment with the apple and grass 
there have been several investigations with other plants to show 
that vegetable organisms have interdependence other than 
those with their physical environment. The Bureau of Soils 
of the United States Department of Agriculture has published 
a series of interesting investigations bearing upon the problem 
of plant excretions.!® Hunt and Cates*® show in a bulletin of 
the Cornell Agricultural Experiment Station an antagonistic 
effect between corn and weeds. Studies on the effect of weeds 
in corn made by Dr. Sturtevant! at this Station in 1883, 1884 
and 1886, show this antagonism, although the cause of the 
malign influence was not assigned to toxicity. At the second 
annual meeting of the Society for Horticultural Science the 
writer read a paper” on “The Relationship of Plants” in 

See page 445. 
*U. 8S. Dept. Agr., Bureau of Soils, Buls. 22, 28, 36, 40 and 47. 
2° New York Cornell Exp. Sta. Bul. 247:188. 
1 Ann. Repts. of this Station, 1883:137; 1884:100, and 1886:50. 
* Proceedings of the Society for Horticultural Science. 1905:72. 
