280 KNuDSON: CAMBIUM DEVELOPMENT IN AMERICAN LARCH 
figures refer to tree A. The figures from June 3 to July 6 refer 
to tree C. 
TABLE III 
NUMBER OF ROWS OF NEW XYLEM CELLS FORMED AND DIAMETER OF NEW XYLEM 
TISSUE IN TREES A AND 
aA May-25 June 3 June 15 June 30 July 6 | 1909 | 1910 
Region of cutting Bee be . eee | | p; 2 Rl worn ewes Dia. 
No. No. aa) No. | ay | No. | — | No. | — | pe 8 
Below 1st whorl ..| o 15 | 262 | 25 544| 43. |1,054! 646} 986 
Below 2d whorl . ° 3 833! 55 1,564, 1,598|1,377 
Below 3d whorl 0 = [20° - }°578"1.33 48 |1,462 | 1,853|1,870 
ow 4th whorl co) 29 | 697 | 43 |1,122| 50 |1,462 1,785|1,870 
Below 5th whorl o 28 | 748| 45 (|1,292| 55 1,530! 1,360/1,955 
Below 6th whorl re) 23 646 | 46 (1,326) 58 ,666 I,275|1,224 
Below 7th whorl te) 24 | 648 | 36 |1,122] 57 3 734|/1,.428 
Below 8th whorl..| 0 22 | 714/36 11,156)57 (1,632,65 1,972|2,363/1,59 
Below oth whorl..|  o 1 607+) a8 | 50) | — | 62 /|1,870/1,666]1,088 
Below roth whorl. oO 20 | 663 | 27 | 833/58 (1,564 58 (1,802 
| | | | | — beac 
Average... i... | O°) 22-5 (636 }-35.2 999.6. 53-3 1,493 61.6 |1,881 1,586 1,488 
y | 1 eee 
From the table it cannot be determined exactly in which part 
of the tree xylem growth first begins. The greatest growth by 
June 3 was below the fifth whorl of branches while the least growth 
was just below the first whorl of branches. In general, by June 
3 more xylem cells were formed in the middle of the tree than at 
either the top or base. This would tend to indicate that the first 
growth of xylem occurred in the middle of the tree below the fifth 
whorl of branches. 
TABLE IV 
NUMBER OF ROWS OF NEW XYLEM CELL 
S AND DIAMETER OF NEW XYLEM TISSUE IN 
TREES B anp D 
May rr May 25 June 8 | June 18 
Region of cutting ar age nee 4 TRSNEP 
Nos Me | | No: aire ee gone 
Below 1st whorl. 205605222 o ty) (3) 22 442 43 | 1,003 
Below 20 whort, . 4.05 5.553 0 ce) 0 40 647 53 | 1,326 
Below 3d whorl, 02: (3) ts) o — — 55 1,394 
Below: 4th whorl. 0. 0 4 ia: 35 918 50 1,258 
Below: sth what. 3. 5 8. o —_—- |— — 45 | 1,202 
Below 6th whorl. ............ ° 5 55 32 850 46 | 1,122 
Below 7th whorl........-.... oO 2 20 — sie 55 1,258 
Below 8th whorl............. oO 0 to) 34 850 -- — 
Below oth whorl............. 0 ° ° 30 782 50 | 1,292 
Below. roth whorl... oO r9) o 49 1,292 
Average 45 Uc a ee ° 1.2 14 32 nas |! ag 4 -3aa8 
