from the pattern: “Daisy Mercerized Crochet Thread, Art. 65 was used in the model. One skein size 20, for one doily (pretty in sets of three). Color may be used very effectively in the last two rounds“

A doily in 17 rounds features:

tr and tr clusters
chain in chain
triple triple crochet (yarn over 4 times)
double treble crochet clusters

Note: In Round 15 each pyramid of tr will be completed separately and finished in rounds 16 and 17.