Callus Formation in Hibiscus Rosa-sinensis L.and Hevea brasiliensis Mü. Arg

Abstract

Studies of callus development on stripped surfaces on both plants, and cleft-grafts of H. rosa-sinensis, show that the cambium takes no part in the early development of the callus cushion which is formed predominantly from the medullary ray system. This formation and development are seen in simplest form on stripped surfaces. There is no sign of cambial activity until the callus cushion is completely laid down. Both bark callus and wood callus are developed largely from medullary ray elements; their respective contributions towards the formation of the callus cushion are pointed out. It is shown in cleft-grafts of H. rosa-simnsis that the contribution of callus tissue by the scion is approximately equal to that made by the stock. The origin of callus tissue from the bark with a smaller contribution from the zone bounding the pith is shown in cleft-grafts of H. rosa-sinensis. The commencement of cambial activity at the points where the ends of the severed cambial ring impinge on the callus cushion, and the ingrowth of the ends of the cambial ring till the two unite in the middle of the callus cushion are descr. The functions and situation of the medullary rays lend support to the view that the simple method of tissue regeneration descr. here will be found to be common in woody plants.