Here's a pic of the underbelly/WS of the rose through the end of Round 3. The chain loops are lying on top of the petals.
In the first round, each of 6 chain loops had 3 ch's. In the third, each of 6 chain loops had 5 ch's. In the second round, each of 6 petals had 3 dc's. You can probably guess how many dc's for the fourth round. From the American Thread Company booklet:
"4th Row. In each loop work 1 sc, 1 sdc, 5 dc, 1 sdc, 1 sc." (sdc -- or short double crochet -- is the same as hdc)
Here is a picture from the RS of the rose with 3 petals made plus part of a fourth. You can see how the base of the petals in this round is hidden beneath petals from the 2nd round. Also, notice that, to make it easier to crochet, I've bent a petal forward. Finally, as with the 2nd round of petals, I need to scoot the sts over to make room for more in the chain loop.
Next week will be the last 2 rnds of the rose -- under the title "Why 6?".