抄録
The effects of the moisture content in midribs during the drying process of tobacco leaves while curing were studied.
1) Surface areas, moisture contents, and such other factors which are necessary to describe the drying process were determined for separated midribs and laminae respectively.
The moisture in midribs represents about a third of the moisture in the whole leaf. The amount of moisture per unit surface area is about ten times larger in midribs than that in laminae. Within the midribs, over 90% of the total moisture is concentrated in the cortex tissues.
2) In the early stage of curing, the moisture content of laminae was almost unchanged although the moisture content of midribs decreased considerably.
When midribs or laminae were separately subjected to curing, the water loss from the midribs was not so large, whereas the moisture content of laminae decreased markedly. Those results suggest that, in the early stage of curing, some of the water in the midribs is transferred into the laminae, where it is vaporized into the free air. In one of the experiments, leaves were subjected to curing to some extent and the leaves were then examined on their ability of water reabsorption. The results showed that, both in lamina and midrib, the majority of the cells maintained their water transfer activity during the curing.
3) To see whether the osmotic action participates in the generation of the driving force or not, the osmotic pressures of the cell sap obtained from midribs or laminae during curing were determined. throughout the experiment, the osmotic pressure of laminae was alway higher than that of midribs, indicating that the osmose had an important role in the movement of water within the leaves. The most probable reason for the higher osmotic value in the laminae seems to come from the saccharization of starch during curing. This conception was supported by a microscopic observation of leaf segments, where starch granules were gradually reduced both in number and size.
