THE EFFECT OF COLCHICINE ON ROOT MITOSES IN ALLIUM

Abstract

1937) had made the sensationalA discovery of the induction of chromosome doubling by colchicine treatment it became a question of prime importance to investigate the cytological mechanism causing this doubling.It has long been known that colchicine acts disturbingly on the normal course of mitosis (DIXON, 1905).DUSTIN (1934) and LITS (1934) regarded colchicine as a very active agent for increasing the numher of mitoses in a tissue (a ,poison caryoclasique,).LUDFORD (1936), however, came to the conclusion that the increase in the number of the mitoses after colchicine treatment was due to an ,accumulation of arrested mitoses)) rather than to a stimulation process.He attributed this effect to a ,failure of the mitotic spindle to form and function in the normal manner)).NEBEL and RUTTLE (1938), who first studied the effect of colchicine on plant cells (stamen hairs of Tradescantia), arrived at a similar result.The material of the experiments dealt with in the present paper consists of root tips of Allium fistulosum and Cepa.Root tips of A. fistulosum were secured from bulbils that had overwintered in the field, while in the case of A. Cepa large bulbs were used, The fistulosum form used had a hybrid chromosome garniture, consisting of somatically 15 medially attached chromosomes and 1 typical fistulosuni s1 (LEVAN, 1936, Fig. 1 b).The Cepa form had the chromosomes characteristic of this species, viz.14 medially and 2 subterminally attached chromosomes (LEVAN, 1. c., Fig. 1 a ) .Bulbs with rapidly growing root tips, O , .s l , o cm in length, were immersed for exposure into colchicine solutions during periods of different length.Root tips were then fixed at certain intervals after the transfer of the bulbs from the colchicine solutions into pure water.The fixations were made in NAVASHIN under air evacuation.The material was embedded and cut into transverse and longitudinal sections, the former being 20 ,u in thickness, the latter 20-30 p.The slides were stained in gentian violet, some also in ,lichtgriin,.The experiments were arranged in the following way.