The palace-gates of gloomy Dis
Stand open day and night;
But upward to retrace the way
And pass into the light of day,
There comes the stress of labor; this
May task a hero's might."
CONINGTON, _AEneid_, BOOK VI.

Nevertheless if AEneas were still determined on this perilous journey
she was willing to aid him and be his guide. But one thing, she said,
must first be done. In the woods around the cave was a tree on which
grew a bough with leaves and twigs of gold.

No mortal could enter Hades without this bough to present to
Pro-ser'pi-na, the queen of Pluto. When the bough was torn off, a
second, also of gold, immediately sprung up. It had to be sought
for diligently, and when discovered it had to be grasped firmly with
the hand. If the fates should be favorable to the enterprise, the
bough could be plucked easily; otherwise, the strength of man could
not tear it from the tree, nor could it be lopped off even with the
sharpest sword.

Here was a formidable difficulty. How was AEneas to find out the
wonderful tree? The Sibyl told him only that it was in the woods, and
the searching might be long and fruitless. But again his never-failing
friend came to his aid. While he was searching the wood with some of
his companions, two doves suddenly appeared, and alighted on the
ground before them. AEneas knew that they had come from his goddess-
mother, the dove being the favorite bird of Venus.