under city conditions, rests as an especial duty upon 

 a botanic garden located in a great metropolitan center 



like New York. Not only must 

 Tree Problems and i "\ 1 11 • r 



Botanical Garden we sol y e these Problems if we are 

 to maintain our Garden planta- 

 tions, but, in view of our relations to the city as a mu- 

 nicipal institution, the park department and all those 

 interested in beautifying the city by street planting 

 have a right to look to us for authoritative advice on 

 such matters. The study we are beginning on the growth 

 requirements of the hemlock is directed to the solution 

 of one of our own most immediate problems, and should 

 be extended to cover the basic physiological and eco- 

 logical experiments outlined above. 



It might here be added that much that is said above 

 concerning the problems of trees applies equally well to 

 many other plants. 



Some Problems of Soils 



The soil in which plants grow offers many fruitful 

 problems for investigation, other than those mentioned 

 above in connection with trees. These relate especially 

 to the two material constituents of the soil: its chemical 

 substances and its living micro-organisms. 



It is well established that the mere demonstration by 



chemical analysis that any particular chemical element 



is present in the soil does not 



Chemical Constituents . , ,1 • , • . • -i 11 , ,1 „ 



f s ., imply that it is available to the 



plant. One of the most important 



problems in maintaining soil fertility concerns the 



potash supply. Potassium may be present in abundance 



in soils and yet not be available to crop plants. There is 



some evidence that so-called green manures are an 



effective means of increasing the availability of potash, 



[13] 



