  The nature of molecular transmitter imposes some limitations on the molecule
production process and its storage. As the molecules act the role of the
information carriers, the limitations affect the transmission process and the
system performance considerably. In this paper, we focus on the transmitter's
limitations, in particular, the limited molecule production rate and the finite
storage capacity. We consider a time-slotted communication where the
transmitter opens its outlets and releases the stored molecules for a specific
time duration to send bit "1" and remains silent to send bit "0". By changing
the release duration, we propose an adaptive release duration modulation. The
objective is to find the optimal transmission release duration to minimize the
probability of error. We characterize the properties of the optimal release
duration and use it to derive upper and lower bounds on the system performance.
We see that the proposed modulation scheme improves the performance.
