  We report optical and infrared spectroscopic observations of the Type Ia SN
1999ee and the Type Ib/c SN 1999ex, both of which were hosted by the galaxy IC
5179. For SN 1999ee we obtained a continuous sequence with an unprecedented
wavelength and temporal coverage beginning 9 days before maximum light and
extending through day 42. Before maximum light SN 1999ee displayed a normal
spectrum with a strong Si II 6355 absorption, thus showing that not all
slow-declining SNe are spectroscopically peculiar at these evolutionary phases.
A comparative study of the infrared spectra of SN 1999ee and other Type Ia
supernovae shows that there is a remarkable homogeneity among the Branch-normal
SNe Ia during their first 60 days of evolution. SN 1991bg-like objects, on the
other hand, display spectroscopic peculiarities at infrared wavelengths. SN
1999ex was characterized by the lack of hydrogen lines, weak optical He I
lines, and strong He I 10830,20581, thus providing an example of an
intermediate case between pure Ib and Ic supernovae. We conclude therefore that
SN 1999ex provides first clear evidence for a link between the Ib and Ic
classes and that there is a continuous spectroscopic sequence ranging from the
He deficient SNe Ic to the SNe Ib which are characterized by strong optical He
I lines.
