Until quite recently only two band-systems had been attributed to compounds of beryllium, BeF being the emitter of one system, which occurs in the ultra-violet, and BeO that of the other system, which lies in the visible region. The former molecule is one of a series of thirteen-electron emitters known band-systems, namely, CN, N 2+ , CO + , BO, BeF, and MgH. The other molecule BeO is of interest on account of the fact that, like the emitter NaH, it has the same number of electrons (twelve) as C 2 , in which an electronic transition 3 P → 3 P is responsible for the emission of the Swan band-system. The observations recorded in the first part of the present paper were made order to ascertain whether any further bands might be attributed to BeF and BeO. The description of the newly observed bands (in section 4) is, for convenience, preceded by a discussion of the known systems. In the course this discussion the data for BeF band-heads are re-examined and a modified interpretation of the heads is suggested (in section 2); and some corrections and additions to, the band-head data for the BeO system are also made (in section 3).