Increase In Elongation Rate Research Articles

Elongational Viscosity of Nonlinear Elastic Dumbbell Suspensions

The Kramers method for analyzing bead-rod suspensions in potential flow has been extended to a suspension of inverse-Langevin-spring dumbbells in elongational flow. The elongational viscosity and root-mean-square bead separation for two different inverse-Langevin-spring models are calculated numerically and presented in graphical form. The numerical calculations for one model are in excellent agreement with similar, approximate calculations made by Peterlin. For linear (Hookean and Fraenkel) spring models with finite spring constants, the elongational viscosity and mean-square bead separation are unbounded, but for both inverse-Langevin-spring models these quantities approach an upper bound with increasing elongation rate.

Effect of Gibberellic Acid and Cycocel on Tryptophan Metabolism and Auxin Destruction in the Sunflower Seedling

AbstractA comparative study of tryptophan conversion in different regions of the sunflower seedling indicates that the regions most active in converting tryptophan on a pathway to auxin are the root apical segments and young leaves; next highest in activity is the cotyledonary tissue. The stem apex proper with leaf primordia is less active than the above regions in converting the auxin precursor. Hypocotyl tissue was observed to be least active. Pre‐treatment of the apical bud region of the stem with gibberellic acid (GA) gives rise to tryptophan conversion rates which are 2.1 times those in untreated seedlings. The enhanced tryptophan conversion in the apical bud is followed by an increased elongation rate of the 1st internode which is 2.2 times that in the 1st internode of untreated seedlings. Treatment of the seedlings with Cycocel [(2‐chloroethyl)trimethylamnionium chloride] does not reduce tryptophan conversion in the apical bud region of the seedling although elongation of the stem is greatly retarded.Indoleacetic acid (IAA) destruction in cell free preparations as well as in whole sections of the elongating region of the seedling stem was studied. IAA‐1‐14C destruction rates with the release of 14CO2 in whole sections of 1st internode tissue were approximately 3 times those in cell free preparations of the same region. No significant changes in IAA destruction rates in seedlings pre‐treated with GA or Cycocel were observed.

Developmental Anatomy of the Fruit of the Deglet Noor Date

1. The development of the fruit of the Deglet Noor date from pollination to maturation in 1941 was divided into seven periods. The calendar dates for each period refer to the fruits examined in 1941 and may be expected to vary somewhat with the district where grown and in different growing seasons. 2. Period I, from March 18 (pollination) to April 30, is an interval of little enlargement, during which some cell division occurs throughout the mesocarp. Period II, May 1 to 23, is initiated by organization of a meristematic zone at the base of the fruits. Cell division ceased in the apical half of the mesocarp by May 8. At the close of this period the endosperm, previously free-nuclear, became cellular. Period III, May 24 to June 15, is initiated by a sharp increase in rate of enlargement of the entire fruit and all cells of the mesocarp, including those of the basipetal meristem, which, however, continue to divide. At the close of this period the fruits become susceptible to checking (minute cracks involving the cuticle, epidermis, and outer cells of the hypodermal layer). Period IV, June 16 to July 13, begins with inactivation of the basipetal meristem of fruits destined to mature earliest and ends when a meristematic zone is no longer present in any of the fruits. This period is also characterized by the highest rate of fresh-weight increase of the season. Period V, July 14 to August 22, starts with a marked increase in rate of elongation of the previously meristematic cells at the base of the fruits and ends as those cells approach maximum length. At the end of this period the fruit is no longer susceptible to checking, and the color changes from green to pink. Period VI, August 23 to September 21, is distinguished by little apparent anatomical change. Marked increase in percentage of dry matter occurs. Period VII, September 22 to November 3, is characterized by softening as a result of continued dehydration of the fruit and partial dissolution of cell walls. The color changes from pink to brown.