50 Years Ago

Despite some impressive demonstrations of root-pressure, 'pumping' or positive pressure is generally thought to be of little importance for the ascent of sap in trees ... In ten species of palms at Calcutta I was able to detect and measure positive root-pressures throughout the year, sometimes enough to lift sap to heights exceeding that of the trees ... The positive pressure exceeds the negative pressure considerably. It often exceeds the plant's needs ... The distal part of a cut root of a fruited banana plant was seen to develop pressure. The plant was decapitated at 2.25 m. above ground-level, and the cut root reconnected with a rubber tube. Other agencies such as transpiration are probably less important than root pressure.

From Nature 21 October 1961

100 Years Ago

My attention has been directed to three elm trees at Ettington ... which it is said have been “killed by wasps.” It appears that the wasps were attracted by the sweetness of the sap, and attacked the trees in such swarms, and so drained them of sap, that the death of the trees seems imminent, all the leaves having gone yellow long before the usual time. I should be glad to know if others have noticed attacks on elm trees, and whether the averred sweetness of the sap is due to some previous degenerative change in the tissues of the tree, or whether wasps would attack a normal tree if they could get access to the sap. The elms are all three comparatively young trees, and belong to the common variety. My informant tells me that he has previously noticed the same thing happen with an elm tree in one of his fields, which died the next winter.

From Nature 19 October 1911