2 8o THE PLANT WORLD. 



green-house before being transplanted to the garden. The 

 soil was carefully cultivated and watered as often as neces- 

 sary during the growing season. In spite of this excellent 

 care it will be noted that the plants around the base of the 

 tree made a poor growth and those closest to the tree were 

 finally pulled up on account of their failure to grow. The 

 illustration shows that the plants in each row were regularly 

 larger as tlie distance from the tree increased, until, at a dis- 

 tance of eight to twelve feet, no more dwarfing effects were 

 evident. 



The cause of the diminished growth near the base of 

 the tree cannot be entirely ascribed to the lack of suitable 

 plant nutrients for, as stated above, the garden received a 

 uniform application of stable manure. Neither can it have 

 been due to the removal of water by the tree because the 

 poorest plants were closest to the tree and hence not in com- 

 petition with the most active zone of fibrous tree roots which 

 obtain most of the food and water supply for the tree. 

 Furthermore, water was applied as often as necessary to 

 maintain the optimum conditions for plant growth. The 

 effect of shade can not be considered as one of the main causes 

 of dwarfing, at least in this case, because the Kentucky Coffee- 

 tree does not cast a dense shade. Furthermore, the poorest 

 plant growth occurred on the south and south-west of the 

 tree, where scarcely any shade was cast. 



If, then, the various physical factors can not be re- 

 garded as mainly responsible for the poor growth of the 

 surrounding plants, it is evident that one must look to the tree 

 itself as the malignant factor. The most important factor 

 which can exert a malignant effect upon the soil at the base 

 of the tree appears to be the washings from the bark of 

 the tree. It is evident that the soil at the base of the tree 

 must receive most of the rain water which trickles down the 

 branches and trunk of the tree. During heavy rains small 

 pools may be formed about the base of a tree, from which the 

 water percolates through the soil or flows over the surface. 



