42 



exclusively in the most recently unfolded growing portions at the tips 

 of the stems, it was evident that the rapidity of increase in the leaf 

 area would at least indicate the frequency with which spraying would 

 have to be repeated in order to keep in a poisoned condition the very 

 limited portion upon which the weevils fed. 



Although the observations were made after midsummer, the plants 

 used were of the right size to indicate the points. desired. Two series, 

 each including five average plants, were selected. 



The plants used in Series I had 8 leaves at the time of the first 

 observation. Those used in Series II were older and averaged about 

 30 leaves each. The leaves borne upon the main stem were classed 

 as primary and those from side branches as secondary leaves. Upon 

 the date of each of the 5 observations made, the number of leaves in 

 each class was ascertained, an average leaf in each class was quite 

 accurately measured, and the total product of numbers and area thus 

 found was considered as the approximate leaf area of the plant. The 

 error has been reduced as much as possible by taking an average of 

 the 5 plants in each series as representing a typical plant, and it is 

 with these results that comparisons have been made. 



Table IX. — Estimated increase in leaf area of cotton, averages of five plants. 



Date of examination. 



Primary leaves. 



Average 



number 



per 



plant. 



1902 



Series I: 



August 30 



September 13 



September 25 



October 6 



October 17 



Series II: 



August 30 



September 13 



September 25 



October 6 



October 17 



10 



Average 

 area, 

 plant. 



Sq. in. 

 64.0 



Percent- 

 age of 



daily in- 

 crease. 



136.8 

 231.6 

 309.6 

 376.6 



177.2 



8.0 

 5.4 

 3.0 

 2.0 



229.2 

 241.6 

 214.8 

 216.8 



2.0 



.04 

 a-1.0 



Secondary leaves. 



Average . 

 number A I^ age 



per 

 plant. 



0.0 



8.0 



16.6 



21.6 

 24.8 

 42.4 

 52.6 



67.4 



plant. 



Sq. in. 



41.2 

 187.4 

 347.8 

 522.4 



341.4 

 514.0 

 619.2 



808.8 



Percent- 

 age of 



daily in- 

 crease. 



30.0 

 7.8 

 4.6 



2.0 

 3.6 

 1.8 

 2.1 



a Decrease of 1 per cent due to falling of old primary leaves. 



Several facts are evident from an examination of this table. After 

 the plant has acquired about eight primary leaves the formation of 

 branches and of secondary leaves began, thereby multiplying the 

 number of growing points. From this time on the greater part of the 

 increase in leaf area took place in the secondary leaves. By far 

 the most rapid period of leaf growth occurred at about the time when 

 squares first began to form. In Series I the average total leaf area 

 practically doubled every ten days through the seven weeks under 

 observation. In Series II the plants were older to start with, and it 

 required about forty days to double the leaf area. 



Everyone now concedes that it is useless to attempt the spraying 

 of full-grown cotton such as is represented in Series II. The extreme 



