Harry F. Clements 453 



data were assembled — and this involved well over 100,000 items — each 

 tissue was examined statistically to permit the selection of the most 

 reliable tissue for each of the materials considered cogent to the prob- 

 lem. As a result, the leaf sheaths of the young mature leaves (leaves 

 3, 4, 5, and 6, counting down from the tip leaf as number 1), were 

 found to be the best tissue for tissue moisture (5), total sugars (6), 

 potassium (4), phosphorus (j), calcium, and magnesium. In addition, 

 the fluctuations in the size of this sample reflected remarkably well the 

 girth of the stalk being laid down at the time the sample was taken. 

 The green tissue of these same leaves was best for use as an index to 

 the nitrogen status of the plant (7). 



During the four years in which these collections were made, measure- 

 ments of labeled pilot plants were made for vertical elongation. The 

 rate of new leaf emergence and the length and width of leaves were 

 determined. 



INFLUENCE OF NUTRIENTS, MOISTURE, AND OTHER GROWTH FACTORS 



After having determined the most reliable tissue to be used as an 

 indicator of the crop's welfare, the next stage of the work involved the 

 determination of adequate levels of nutrient materials and moisture. 

 These experiments were, for the most part, conducted on the planta- 

 tion. The results of these studies show that for potassium, 2.25 per cent 

 is the adequate level for the heaviest as well as the lightest production 

 areas (4). For phosphorus 0.080 is the adequate level {4). Not enough 

 work has been done to fix the levels for calcium and magnesium, but 

 these two materials have not as yet been found to affect cane yields in 

 Hawaii. 



The correct levels for nitrogen vary rather markedly from area to 

 area (j, 6). In general, the lower the temperature of the area, the higher 

 the nitrogen index of the cane leaves. To be sure, it will take less nitro- 

 gen as fertilizer in cool areas to raise the nitrogen index than it will in 

 areas of heavy growth. The relationship between the nitrogen index 

 and the moisture index is so intimate that it is usually easy to determine 

 the correct nitrogen level from actual tissue moisture levels. This applies 

 not only to different climatic zones but also to different varieties within 

 a zone. 



