Studies on the Relation of the Living Cells to the Transpiration and Sap-Flow in Cyperus. II

Abstract

1. Stems of Cyperus cut and placed in water wither sooner than when a certain portion, not to exceed 20 cm., has been killed by steam. 2. When 20 cm. of the stem are killed by steam, the leaves wither in about 8 days, that is, in about the same time as the control plants. 3. The longer the portion of the stem killed with steam, the sooner the leaves above wither and dry. When 25 to 30 cm. of the stem are killed with steam, the leaves wither in 3-5 days. 4. No matter how long the section killed may be, the leaves on steamed stems never wither quite so quickly as those cut and not placed in water, but under the same conditions of light, temperature, and air moisture. 5. In Cyperus sufficient water to maintain the leaves turgid for 3-18 days will rise through a stem 15-60 cm. high, with a section 5-30 cm. long which has been killed with steam. 6. A certain amount of water is raised through the steamed portion, but it gradually diminishes in quantity from day to day, until the leaves become air dry (about 11 per cent of their dry weight of moisture). 7. The diminished water supply is partly due to a partial blocking of the vessels with a gumlike or resinous substance, which probably owes its origin to the disorganization of the contents of the sieve tubes caused by heating the stems. 8. The withering of the leaves above a steamed portion of the stem is probably caused more by the action of deleterious substances introduced into them from the dead cells than from lack of water. These poisonous substances are probably disorganization products caused by heating with steam. 9. The leaves of rooted plants, grown in nutrient solutions containing sterilized decoctions of the same plant, droop in 3-5 days, discolor and dry in 7-8 days. 10. The withering leaves above a portion of the stem killed with steam show all the symptoms of dying, namely, rapid loss of water after treatment, then a more uniform loss, rounding up and discoloration of the chloroplasts, and contraction of the mesophyll protoplasts. The leaves are apparently drying, not so much from lack of water as on account of the death of the cells from other causes. 11. Judging from the behavior and disorganization of the leaves on a stem, a section of which has been killed with steam, it is evident that this method of killing the cells is not a satisfactory one in order to settle the question as to the relation of the living cells to sapflow. 12. Killing a portion of the stem by applying wax heated to 110⚬ C. causes less apparent disorganization of the cells, less injury to the leaves above, and does not cause a marked immediate decrease in the transpiration. 13. Experiments in which 5-10 cm. of the stem are killed by treatment with picric acid, 95 per cent alcohol, or CuSO4, for 36-48 hours show that sufficient quantities of water may ascend through the poisoned portions to supply the transpiration need for a comparatively long period (90 days), and to allow the development of new branches. 14. Certain poisons (picric acid, chromic acid, and HgCl2) may greatly accelerate the amount of water evaporated in poisoned plants. Not all poisons act alike in this respect; HgCl2 causes the greatest amount of increase in water loss.