Abstract
THE capacity possessed by the roots of certain parasites, such as Cuscuta, to penetrate into the tissues of their host, is apparently an unique, not to say a remarkable phenomenon. A little reflection, however, upon the powers of roots in general, leads us to doubt whether this property is really as restricted as the first glance would lead us to imagine; and when we peruse Prof. Pfeffer's work upon the pressure of the root, and find that, for instance, the root of the common bean exerts during its growth a pressure of some 400 gms., we realise that this mechanical action alone might suffice to drive the growing root of most plants into living tissue, if circumstances necessitated such an expediency. This is evidently an important point, and touches upon the evolution of the higher parasites; it is only remarkable that it has so long remained untouched. We must now thank George Peirce for taking up this neglected subject, and placing it upon a sure basis (see Bot. Zeit. September 1894). The question first to be decided was whether the pressure which Pfeffer had found in the growing roots was in itself sufficient to force the roots through living tissue. For the determination of this, iron models of roots weighted up to 270 gms. were employed. The apices of these were placed upon a cube cut from a potato, and the whole surrounded with damp sawdust to keep the living substance fresh. After an interval of twenty-three hours, it was found that the iron point had penetrated 1½ m.m. into the potato. Again, a similar model weighted to 320 gms. was driven in twenty-four hours through the cork layer and 2 m.m. of parenchyma of an uncut potato. Also a root-model placed on the stem of Impatiens sultani, one and a half centimetres thick, pierced this in less than twenty hours when 300 gms. weight were employed.
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BEER, R. The Penetration of Roots Into Living Tissues. Nature 52, 630–631 (1895). https://doi.org/10.1038/052630a0
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DOI: https://doi.org/10.1038/052630a0