My interpretation of this is that the author was hoping for something futile - they 'grew a flower' (put effort or hopes toward) that can't be bloomed (is pointless or futile, will not produce anything) that can't come true (their effort/hope is just a hopeful dream). Basically, the author hoped for something that was not possible.
Answer:
Early cave art shows that people had advanced knowledge of the night sky within the last ice age. Hopefully this helps!
Dotted half note is the answer.
