155 



'99, p. 688), and on the higher sand-hills is certainly much 

 lower. It is here beyond the reach of all plants except the 

 larger trees, and they, too, must be able to live in the poorer 

 surface sand until their roots have penetrated nearly to the 

 level of the ground-water. 



The importance of the relation of food supply to vegeta- 

 tion has probably been greatly underestimated, while too much 

 stress has been placed on the water supply and the physical 

 condition of the soil. Whitney and Cameron ('03) have even 

 declared that all ordinary soils contain plant food sufficient foi 

 the growth of crops, and this may well be so in a soil contain 

 ing relatively large amounts of calcium, potassium, magnesium, 

 and phosphorus, even though little may be available at any 

 one time; but in a sand composed in very large proportion of 

 silica, the leaching action of the rainfall must ultimately tend 

 toward the exhaustion of the plant food, leaving a residue of 

 silica and other insoluble substances. Such has been found the 

 case in various places. Livingston ('05, p. 26) has remarked 

 upon the low content of soluble salts in some sands in north- 

 ern Michigan. Graebner ('01, p. 64) has discussed the leaching 

 action of rain on the sandy soils in Germany, and decides that 

 the formation of heaths there is due in great part to the insuffi- 

 cient supply of plant food. No full determinations of the solu- 

 ble matter in the Miami fine sand have as yet been made, but. 

 according to Professor Mosier, this sand is deficient in plant 

 food of all kinds. The relative height of plants growing in 

 Mason county on sand and on loam soils, certainly indicates a 

 scarcity of plant food in the former. Indian corn tassels on 

 the sand at a height of three to four feet; Monarda punctata is 

 usually little over a foot high; and many other species are con- 

 spicuously below the size reached in the neighboring woodl- 

 and on the prairies. 



Unfortunately none of the foregoing theories has been 

 tested by actual experiment on sand plants in the region un- 

 der discussion, and until more definite knowledge is available, 

 one can only believe that in general the supply of food matter 



