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We have obtained HST Planetary Camera observations of a total of fifty-threelow-mass (M < 0.3 M_solar) members of the Hyades cluster. Nine of these starsare resolved as binaries, with separations between 0.1 and 3.1 arcseconds,while a further three are probably equal-mass systems at smaller separations.Allowing for observational selection effects, this corresponds to an observedbinary fraction of 11.3 plus or minus 4.6% for systems with separations in therange 14 to 825 a.u., consistent with observations of solar neighbourhoodM-dwarfs. The mass-ratio distribution is only consistent marginally with thesecondary stars being drawn from a Psi(M) proportioal to M^{-1} mass function,with three equal-mass systems amongst the six binaries with observedseparations in the regime where our observations extend below thehydrogen-burning limit. Considering the entire sample, the absence of any browndwarf companions amongst our sample makes it unlikely that the mass function ofstellar/brown dwarf companions rises as steeply as M^{-1}. If the Hyades has anage of 600 Myrs, our results are consistent only at the 2 sigma level with aflat (M^0) mass function.Comment: 19 pages, 2 figures, AASTeX, to appear in the December 1997 A

Low-Mass Binaries in the Hyades: A Scarcity of Brown Dwarfs