Fluid crystals and meristematic growth.

Abstract

In an attack upon certain phases of the problem of meristematic growth, a cytological investigation of the cells of the squash root tip was made. Tissues fixed in fluids which preserve lipoidal structures, such as formalin-bichromate mixture, and osmic acid revealed structures which warrant description.

The growing tips were fixed by two to three weeks impregnation in 2 per cent osmic acid, after the Kopsch-Mann technique. The sections were mounted in balsam unstained. In such preparations there appeared granules of varying sizes but of uniformly high refringency. These granules were practically round, and in ordinary light the centers appear lighter than the periphery. They are present in all parts of the tip. In the growing point they are small and occur from three to six to the cell and are usually clumped in one corner or are arranged along the cell wall. Some cells, however, appear to he devoid of these characteristic granules. In the highly vacuolated cells they are much larger and fewer to the cell than in the tip. In such cases they are almost invariably found to lie at the periphery of the vacuole, close to the cell wall. The object in making these osmic acid preparations was to determine whether any structures are present which might correspond to the Golgi bodies of animal cells. It is not certain whether these granules are actually Golgi bodies. Other granules which are not hirefringent are also present arid the probability is that they represent different stages in the metabolic activity of the cell. There is no evidence of a canalicular apparatus such as Bensley 1 found in the cells of the onion root tip.

When these granules were studied with the polarizing microscope they were found to be uniaxial sphaero-crystals.