“…In these several years, many people have published their results on the qualitative theory of foliations, mainly of class C 2 and of codimension one. These results can be more or less interpreted as those on the realizability or non-realizability of manifolds as leaves having a certain qualitative property (e. g. Sondow [15], Nishimori [10,11,12], Cantwell-Conlon [1,2,3], Tsuchiya [17,18,19], Phillips-Sullivan [13], Inaba [7,8], Takamura [16], and so on). From this point of view, one may naturally ask the existence of open manifolds which can never be realized as leaves of foliations of any closed manifold.…”