The infection of clover root hairs by nodule bacteria studied by a simple glass slide technique.

SUMMARY: A simple glass slide technique has been devised for the continuous microscopical observation of growth and infection of root hairs of clover seedlings. The method involves an aseptic cultivation of seedlings on microscope slides which are partly immersed in a mineral salts medium. The roots are protected by a cover-slip. By this procedure, the root hairs of white clover inoculated with nodule bacteria were studied. The earliest infection was observed to take place within 48 hr. of inoculation, on 4-day-old seedlings. In branched hairs the growth of the thread from a lateral branch towards the hair tip is tentatively explained as an effect of the position of the hair nucleus relative to the site of infection. The infection of leguminous plants by nodule bacteria has, as a rule, been studied with fixed and sectioned material. The first stages of this process may also be studied in vivo, but no suitable technique has yet been described for a continuous microscopical examination of these stages. A method for the study of growing root hairs (of wheat) was devised by Lundegkrdh (1946) and modified by Ekdahl(1953). In their work, a chamber containing flowing salt solution and resting on a microscope stage was employed. However, difficulties arise with this method if aseptic conditions are also necessary. The present author has therefore used a technique for the aseptic cultivation of young seedlings on microscope slides in a manner which permits periodic observations under the microscope of the growth and infection of individual root hairs. The arrangement also offers good conditions for photomicrography .