Growth Studies in Forest Trees. I. Pinus Rigida Mill

Abstract

1. The histological characters of Pinus rigida present no wide variation from the normal coniferous type. 2. The secondary thickening in the root is similar to that in the stem, but differs (a) in less sharp demarcation between the annual rings, (b) in the biseriate character of tracheids, and (c) in less density. 3. Growth began in young 20-30-year old specimens of Pinus rigida in the vicinity of Ithaca as early as April 15. While there was no direct evidence of cambial awakening secured the previous year, sections taken at a later date showed growth in such an advanced state that it must have begun fully as early. 4. In older trees cambial awakening is sometimes retarded at the base where proper insolation is lacking. 5. There is no appreciable difference in the time of cambial awakening on the north and south sides of trees. 6. Growth began first in 20-25-year-old specimens at some distance below the apical shoot, but during a period of 19 days gradually spread upward until it reached the apex of the trees. 7. Investigations on trees A, B, and C tend to show that growth in older individuals begins first in the crown and spreads downward. The time of its inception at the base varies with conditions of insolation, bark, etc. 8. Growth in the branches follows the same rule as in the main axis. The time of awakening in the former is almost if not absolutely identical with that in the latter. 9. Growth spreads down the main axis faster than it does along the lateral shoots. 10. Except in the terminal shoot, growth in diameter was more rapid between May 25 and June 6. In the terminal shoot itself greatest rapidity of growth was manifested between June 6 and June 15. 11. No reliable deductions concerning cessation of cambial activity can be drawn from the present investigations. 12. The width of the complete ring decreases from apex to base; the living portion of the cortex follows the reverse rule. 13. A number of peculiarities already noted by others are prevalent in mature specimens. These are (a) lessened density of wood on the south side of trees, (b) irregularity of cambial awakening in closely neighboring parts of the same section, (c) successive formation of new elements before previous ones have reached their maximum size, and (d) double rings.