The Relation of Pectose and Pectin in Apple Tissue.

IT has long been maintained that pectose, or proto-pectin as it is called by some authors, is an insoluble constituent of plant tissues, associated with cellulose in the cell-walls but exhibiting none of the properties of that substance. It has also been claimed by the majority of investigators that during the ripening of fruit, pectose decomposes into a soluble form, generally known as pectin, which consequently appears in increasing amounts in the expressed cell-sap as the fruit matures. In the unripe fruit, however, pectin occurs in negligible quantities only. Concurrently with this disturbance in the pectic constituents, the fruit exhibits signs of softening as ripening proceeds. Microscopic examination of the tissues shows that this softening is associated with structural relations and staining and chemical reactions of the cell-wall which can only be interpreted as due to the conversion of an insoluble substance like pectose into soluble pectin. In advanced stages of over-ripeness and during senescence the pectic changes become very much pronounced. In this condition the tissues are readily disintegrated, the cell-walls become markedly thinner, and the cells ultimately separate from one another owing to solution of their middle lamella substance. It has been found possible to locate the pectic substances in the cell-walls by staining with ruthenium red, and to follow their distribution throughout the development of the fruit'. Pectic substances have been located in the cell-walls and middle lamella, and periodic examinations of the apple tissue as the season advances confirm the view that the physical modifications in mature fruit are due to pectic changes, and that the processes of ripening and physiological breakdown are intimately associated with the progressive change of an insoluble pectic substance into a soluble modification. As a result of chemical work already published in part [Carr6, 1922] and the unpublished