Altho-ugh a vast amounLt of experimiental work has been devoted to the inhibition of germination and growth of fungi by chemical means, relatively little is known coneerning the influence of various chemicals in the induction of changes in organisms thus inhibited. The subject is not even mentioned in a recent and authoritative book oni fungicides (Horsfall, 1945). In experiments with thymnol and related materials which inhibit growth of Aspergilli and Penicillia, some rather striking effects upon the morphology of gerinilating conidia were noted, and these observations provide the basis of the presenit report. The antifunigal activity of thymol (3-hydroxy-para-eymene) and carvacrol (an isomner of thymnol) was apparently discovered by Myers (1927), who reported that these substances were fungicidal to an unidentified yeast. Shortly thereafter, Kingery and Adkisson (1928) established that thymol in a concentration of one part in 7500 is fungistatic to various dermatophytes, to Sporotrichurn schenckii, and to Coccidioides immitis. In a previous paper (Wolf and Wolf, 1950), it was founld that the growth of a number of Aspergilli and Penicillia was inhibited by thymol and related materials when present in concentrations of 0.025%. The substances tested, in addition to thymol, included carvacrol and Stabilizer #1 (a mixture of monoisopropyl meta and para cresols, produced by the Sindar Corporation, New York, and intended for use as a mold inhibitor for incdustrial starches). Materials and Methods. The fungi studied in the experiments to be reported ineluLded cultures of Aspergillus niger van Tieghem, A. sydowi Bainier and Sartory, Penicihuinm crustosutm Thom, P. cyaneumn Bainier and Sartory, P. cyclopitumn Westling, P. olivino-viride Biourge, and P. waksmanti Zaleski. The muediuLm employed was a modified Czapek's solution containing NaNO3, 3.0 gim.; KH2PO4, 1.0 gin.; MgSO4. 7H2O, 0.5 gm.; KCI, 0.5 gm.; FeC13, trace; and sucrose, 30.0 gm. per liter, having a pH of 4.5. The cultures were ineubated at room temperature. Observations. During previous experiiments, in which it was sought to determine the thymol concentrations fungistatic to a nuumber of organisms,