326 



AMERICAN JOURNAL OF BOTANY 



[Vol. 9, 



centage of ash in the whole plants was still slightly greater in the plants 

 having the greater dry weight. 



This slightly greater relative increase in the ash weight than in the dry 

 weight seems to indicate that when a slightly greater quantity of food is 

 available it is used for additional growth, perhaps largely in building up 

 additional protoplasm. The addition of protoplasm, which is relatively 

 higher in salts than non-protoplasmic structures, might increase the per- 



centage of ash slightly. If, on the other hand, food is produced in excess, 

 as was evidently the case in the tops of the plants grown in the sunlight, a 

 point is soon reached at which the utilization of foods and inorganic salts 

 in the building of protoplasm is limited. The surplus food may then be 

 used in the building of cell-wall material, or it may be stored in some other 

 form. Since cell walls and storage products in plants are usually low in 

 ash content, it is evident that any great increase in the production of these 

 over the production of protoplasm would lower the percentage of ash in the 

 dry matter. 



The last column of table 9 presents the differences in the percentages 

 of ash in the tops, roots, and total plants between the high- and low-trans- 

 piring plant^. In every case the relative increase of ash was higher in the 

 roots than in the tops. Those roots showing the greatest relative increase 

 in ash content are those which also show the greatest increase in dry matter. 



