Apparatus and method for monitoring crops.

A bubble excluder device adapted for use with, and attached to, a probe for continuous measurement of the cell density of a culture in a liquid medium in an aerated fermenter, the bubble excluder device an inlet and an outlet comprising to allow liquid flow through the device, the inlet having a conduit which, in use, is substantially vertical, the conduit comprising means for excluding bubbles creates a path serpentine flow within the conduit means serving bubble exclusion to reduce or prevent ingress of bubbles from the liquid medium outside the device.