Alcatraz of the Starways by Henry Hasse

"Up you go! " Mark's long muscles corded as he heaved and Aladdo's body left the mud with a sucking sound, to sprawl on the solid ground of the island. Presently the Earthman joined him, and for a few seconds they rested silently.

All around them the vegetation surged, lush and matted, inextricably tangled with parasitic vines. Whereas the expanse of swamp was bare of the myriad growths of Venus, for some unknown chemical reason, the island itself was riotous with them. It was as if every inch of _terra firma_ were precious. The humid air was hot and stagnant, heavy with the overpowering fragrance of flowers. Even after two months of conditioning, Mark had difficulty in breathing, as the odors of this alien world increased as the temperature rose.