I tried to find word for Dandy. Could not.
I have enough trouble with Scottish words.
I had Runts as a possible answer but could not parse.
Run is a path, it seems.
...cells contain letters up to and including a certain letter. The 'certain letter' helps! I think a quick grid stare should point you in the right direction, and so should the answers which don't cross the partition (border, line, shape).
Is the shape 2 column wide and 2 rows high at the bottom?
None of the letters go beyond the shaped letter.
Last letter of 35a would be the last letter in the series.
Hankir, Roslyn's post should help you. I forgot to remind you that the 'exactly one third of the grid' should have helped you too. Have another look...
The answer to 39 doesn't cross the partition - a bit sneaky, the preamble... but it didn't lie! My shape is 8 rows down on one side, 4 on the other, and 8 across at the widest point.