Final answer:
To determine which lab sample is positive for the spore stain, observe the slides for endospores appearing green and vegetative cells appearing pink, as seen in Bacillus subtilis, or for other positive characteristics like non-absorption of negative red stain by B. megaterium spores.
Step-by-step explanation:
Identifying the bacterial sample that is positive for the spore stain involves observing the slides prepared using the endospore staining technique. This method is particularly useful for identifying Bacillus and Clostridium species, which are Gram-positive bacilli and produce endospores. When a sample is positive for spore staining, the endospores will typically appear green and the vegetative cells pink, as in the case of Bacillus subtilis. Samples of Bacillus anthracis absorbing crystal violet would also indicate a positive result, as would those of B. megaterium where the spores do not absorb the negative red stain.