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The dikaryon #5026 (A2B2)+#5132 (A7B7) of the basidiomyceteCoprinus macrorhizus was treated with ultraviolet light (UV),N-methyl-N′-nitro-N-nitrosoguanidine (NG), and 5-bromouracil (BU) in order to induced developmental variations in fruiting. Among a total of 11,383 isolates, 742 were homokaryons. Fruiting test was made with the remaining 10,641 dikaryotic isolates, of which 1,594 showed abnormality in basidiocarp development. Both UV and NG were very efficient in inducing such variations, but BU was not. The induced variations were classified into seven basic types as follows: 1) “knotless”, in which hyphal knots, the first sign of fruiting, do not differentiate; 2) “primordiumless,” in which hyphal knots are formed, but no further development occurs; 3) “maturationles”, in which primordia are formed, but the maturation of primordia into adult fruit bodies does not occur; 4) “elongationless”, in which the elongation of stipe is blocked, and a basidiocarp with a very short stipe is produced; 5) “expansionless,” in which pilei do not expand normally; 6) “sporeless,” in which the formation of basidiospores is blocked and albinic pilei bearing none or only a small amount of spores are produced; and 7) “autolysisless,” in which the autolysis of pilei does not appear to occur. It has been noticed that the four steps of maturation, i.e. stipe elongation, pileus expansion, spore formation, and perhaps pileus autolysis, can proceed independently. Compound types of variations such as “elongation-expansionless,” “elongation-sporeless,” “expansion-sporeless,” and “elongation-expansion-sporeless” were also induced. UV treatment induced maturationless at the highest rate, while NG treatment sporeless.