456 Mineral Nutrition of Plants 



studies, the crops were kept above these limits and, hence, these two 

 materials were not included in the statistical treatment. Throughout 

 my work, the sheath moisture level as a physiological factor dominates 

 not only the growth of the plants but also the levels of the nutrients 

 which the plant maintains. It is so dominant that one is forced to 

 wonder at the completeness of fertilizer trials which ignore this factor. 

 The age of the crop shows a strong negative influence. Perhaps age is 

 not so important as height which, of course, parallels age. The total 

 sugars show a small positive influence on the growth units. Soil mois- 

 ture achieves minor significance at this point, although we shall see its 

 true significance later. Light intensity is not a significant factor at this 

 point nor is nitrogen. 



EVALUATION OF GROWTH FACTORS 



Before a complete evaluation of all these factors can be made, it is 

 essential that a measure of influences affecting each of these be looked 

 into. Since growth is determined by morphological structures as well 

 as physiological processes and ecological influences, it is likely that 

 certain factors may not be properly measured when analyzed only 

 against total growth. Thus, for example, radiant energy is shown not 

 to account significantly for any of the variations in growth. Obviously 

 this cannot be true. The same holds true for nitrogen. It is possible 

 that these factors favor one aspect of growth and hamper another, and, 

 thus, in a single analysis would be canceled out, or that the influence 

 of one factor is absorbed by another factor, more dominant in its 

 influence. 



In Table II the above factors are measured against the elongation of 

 sugar cane. 



The factor most closely related to elongation is the rate of leaf emer- 

 gence which is, of course, to be expected since leaf and internode for- 

 mation result in the formation of intercalary meristems and, in turn, 

 compose the morphological mechanism of elongation. The three other 

 dominating factors are sheath moisture, maximum temperatures, and 

 minimum temperatures which are all positive and strong in their in- 

 fluences. The green weight of the sheath tissue, soil moisture, total 

 sugars — all exert significant positive influences while age and nitrogen 



