The Kinetics of Latex Flow from the Rubber Tree in Relation to Latex Vessel Plugging and Turgor Pressure

摘要

Several attempts have been made in the past to express the rate of latex flow from the tapped tree as a function of time and various parameters concerned with fluid flow dynamics. However, no single model that was proposed could explain the regulation of latex flow rate from tapping to flow cessation. In the current study, the cumulative proportion of latex vessels that are plugged at any time, x, from tapping is shown to be proportional to [(x/t)]~(1/2) where t is the total flow duration. This relationship is maintained when latex vessel plugging rate is increased by shortening the tapping cut from (from half-spiral to one eighth spiral) or decreased by ethephon application. It is deduced that about 71% of the latex vessels would have plugged and are no longer contributing to the latex flow by the mid-point of flow duration. About half of the latex vessels are plugged after one quarter of the total flow duration has elapsed. It is also at this point in the course of latex flow that yielding latex vessels are least liable to plugging. The rapid latex flow observed immediately after tapping is attributed to the high turgor pressure (that is of an order of 10 atmospheres) of the laticifer system before tapping. The sharp decrease in latex flow immediately after tapping is explained by turgor loss. On the other hand, the effect of latex vessel plugging, in which lutoid damage plays a role, becomes more prominent towards the end of flow. The plugging rate among latex vessels that are still yielding rises steeply towards the late flow just before flow cessation. The two variables, turgor pressure and cumulative latex vessel plugging, when taken together account for 99% of the variation inflow rate from the time of tapping until the cessation of flow. Since cumulative latex vessel plugging is itself a function of time, latex flow rate can be expressed as a function of the laticifer turgor pressure and time without having to invoke considerations of fluid dynamics, latex vessel contraction or the dilution of the latex that occur during the course of flow.