| Abstract: | Two different greenhouse experiments were conducted to determine the influence of some environmental factors on the increment of the fibrous sheath in the green snap bean pod, using Wade variety. Fiber was determined by the standard Food and Drug Administration method, and measured in grams per 100 grams of green pods. In the first experiment, repeated four times, two levels of calcium (high, 1/5) and three levels of sulfur (high, 1/5, 1/25) were combined factorially with three moisture levels (field capacity, 0.75 F.C., 0.50 F.C.). The base nutrient solution was Hoagland's No. 1. The plants were grown in quartz sand and nutrient solutions were applied as deemed necessary. Moisture was based on oven dry sand with correction for plant weights. Pods were harvested at the No. 5 sieve size and fiber was determined by the FDA method. Results showed significant moisture X nutrient interactions in all but the No. 2 trial, indicating that these two factors do not act independently of each other. Significant differences were also obtained in the last two trials between nutrient levels, and between moisture levels in the last one. In the second experiment one group of plants was grown under simulated summer temperatures (85-95°F), while a similar group was grown under spring temperatures (60-70°F), optimum for beans. Both groups were grown in a regular soil mixture under optimal moisture. Pods were harvested at sieve sizes 2 through 6, and fiber was determined by the FDA method. Results showed that fiber contents of the pods from the hot environment was significantly higher at the .01 level than that of pods from the mild environment. From both hot and mild treatments, samples of pods sieve size 2 through 6 were gathered, killed, dehydrated, and embedded in paraffin; sections were then cut and prepared for anatomical studies. These studies disclosed the fact that increase in fiber in the mature pod occurs by differentiation, via cell wall deposition, of bordering endocarp cells. Increase in fiber may occur prematurely due to high temperatures, such as are prevalent in the summer. A close relationship was found between fiber as determined by the FDA method and fiber as observed anatomically. Indirect evidence indicates that the fibrous sheath later becomes the dehiscence mechanism of the dry pod. Further anatomical studies with very young pods showed that the fibrous sheath in the snap bean arises at anthesis at the outer endocarp and not, as was expected on basis of previous work, at the outer mesocarp. These studies corroborate previous findings by other investigators that the fiber extracted in fiber determinations is the same as sidewall fiber observed in pod sections. |
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