Mimulus have a movable stigma (female part of the flower) which consists of two tiny flat plates, which if touched, close together quickly. The stigma always stands above the anthers (pollen bearing part of the flower). Because mimulus flowers contain both male and female organs, it is necessary to remove the unused parts when breeding them.
You will need small scissors (manacure or moustache),
nail clippers (fingernail or pedicure),
a method of tagging your cross (I use the type
of nylon cable tie used in electronics, which includes
a small area for writing),
a weatherproof marking pen,
tweasers (optional).
1. The first step is to choose the male and female parents. Generally, this is a matter of convenience, but if the flowers differ greatly in size the smaller should be the female for best results.
2. You will record in your record book or computer a number for the cross, and the parents. Each of my plants is numbered and logged. When I make a cross I assign a number for the cross (two digits for the year, and the number of the cross) like this: 99-3 9905 x 9922. In this example, the cross number is 99-3 (the third cross in 1999), and the parents' numbers are listed ladies first (the female parent is 9905 and the male parent is 9922 in this example). I would only record 99-3 on my nylon tag, but list all the information in my log.
3. The male flower selected must be at the correct stage of development. The pollen must be fresh but powdery. If the flower is too old, there will not be any pollen. If the flower is too young, the pollen will not be available yet. Now clip the flower from the plant at the base. Remove the petals from the flower, by gently tearing them off and/or with the small scissors. Carefully clip off the stigma (and single pistil), but do not harm the anthers or stamens. (The pistil is the single filament that rises to the stigma. The stamen are 4 filaments that rise to the small pollen bearing knobs or anthers at the top.) You can now set the male flower aside in a small saucer or dish.
4. The female flower selected must also be at the correct stage of development. It must be unfertilized, and the stigma must be in a receptive state. Easy enough to visually check, since receptive mimulus stigma display the characteristic two flat plates. If the stigma is shriveled or the plates are closed, that means the flower is too old, or was already fertilized. Now you must work with the flower, still on the plant. Carefully cut off the flower petals, being careful not to disturb the stigma. Carefully again, clip off the four stamen (and anthers, which carry pollen), and don't disturb the stigma. When you are done you will have a little stub of a flower and a stigma with its plates still open. (Note: this preparation of a female flower is not necessary when you are selfing the crosses.)
5. Take up the prepared male flower now. Gently touch the anthers from the male flower to the stigma on the female flower. This should transfer pollen to the female flower. If you are successful, the plates on the stigma will quickly close. This is a sign that you have probably made the cross, but set the male flower aside again as a precaution.
6. Tag the female flower, as described above, and record the cross in your log. I use nail clippers to remove the extra nylon strip from the tag after it is closed.
7. Many flower breeders place an envelope over the flower at this stage, but with mimulus this is not necessary. If the cross was successful, the stigma will remain shut and is not receptive to pollen. If the cross was unsuccessful the stigma generally opens again in 15 to 30 minutes. Check back, and if the stigma has reopened, repeat the cross.
[updated 4/11/2000]