What are the white eggs growing from a black stem on the Napa cabbage plant?
I'm no expert in slime molds, but your specimens do in fact look a lot like the sporangia, or spore-producing reproductive structures (i.e., fruiting bodies), of a Mycetozoan slime mold in the class Myxogastria.  Physarum and Comatricha are possible candidate genera based on structure of their sporangia that I can find easily online. 

See below for an example image:



 Sporangia of Physarum pusillum. Source: Wikimedia 

You can see many photos of the white sporangia of Physarum pusillum here and a close-up of the white sporangium of Physarum pseudocolumellatum here

I don't think I can provide a more specific answer given the quality of your photo or my general lack of deeper knowledge of these organisms. Regardless, no quick search for slime-mold infections in plants produced any information regarding slime mold species that regularly grow above-ground on cabbage. 


However, I did find this site which suggests that decreasing the moisture or increasing the salinity of the slime mold's environment will cause it to move along...