Studies on the water relation of Buxus leaves

Summary

Using a fine thermojunction, the freezing points of both of the living tissue and the dead one of Buxus leaves were observed by repeating the treatment of freezing and thawing. The seasonal change in the water content was also observed in parallel with those. Moreover, the process of ice formation in freezing was observed macroscopically and microscopically.

Principal results are as follows:

• 1. The double freezing, which had been frequently observed in storage tissues, was shown markedly in a freezing curve. The double freezing may be a discontinuous phenomenon between the extracellular and the intracellular freezing.

• 2. In the formation of “Frostblase”, the ice was formed on the outside of the cells beneath the veins which may have hight water permeability and grew gradually by obtaining the water from these cells. When the ice piece grew larger, the spongy tissue was easily separated from the stiff layer of veins developing just beneath the palisade tissue.

• 3. The water, participating in an ice formation, was supplied in a considerable amount through a petiole besides the water involved in the leaf itself.

• 4. Even when a leaf was frozen under field conditions, the ice located as “Frostblase” on a distinct part of the leaf, and the intracellular space did not freeze. Therefore, there was no damage.

• 5. In winter, the freezing point of living tissue depended on the solute rather than on the colloidally bound water and was considerably lower than the air temperature.

• 6. In spring, the freezing point of younger or older leaves became considerably high and the freezing of leaves was induced often when the air temperature dropped suddenly. It seems that in Buxus the leaves are adapted to cold temperature because even when the leaves are frozen they form the “Frostblase” and do not suffer any damage.