As Karvannan said, you can call another SP2013 workflow via REST. However, if you are using SharePoint 2013 On-Prem, then be aware that you will require the May 2014 CU. I have tested this before with and without the patch in the past, and without it, the REST endpoints for this will not work.
If you find yourself in the situation of not being allowed to install this CU in your environment (as the client said no in my case), then consider creating an Event Receiver that is attached to the secondary list that will kick off the other workflow on item creation. The reasoning for the auto-start not working is by design to prevent the recursion issue, which is very valid. Fortunately, Microsoft did provide these REST endpoints as the lack thereof would cause common business functionality to be inhibited.