This lace is a mixture of machine-made braid and handmade crochet and was popular in the early twentieth century as a hobby lace. In the piece of lace in the image the braid actually makes up quite a substantial part of the design and the crochet is used to fill the central area of the flower, join the gaps between the flowers, and make a picot edging around the edge of the complete doily.
Therese de Dillmont gives instructions in her Encyclopedia of needlework for making this type of lace and the illustration gives a better idea of how the outer picot edge would have looked when the doily was first made. Also, the piece in the book uses a continuous tape of the medallion braid, which would have made the work quicker, while the maker of the doily has cut the braid and joined it in separate rings to make the individual flowers.
However, I think she probably worked in this way so she could make the flowers individually and then join them all together at the end of the project and finally complete the lace by working an outer crochet edging all the way round the doily.