Peel cucumbers, cut in half lengthwise and scrape out seeds.
Cut into chunks, place in bowl.
Cover with boiling water and add lemon juice.
Soak for 15 minutes.
Soak gelatin in cold water in small cup.
Set cup in simmering water to melt gelatin until clear.
Place cucumbers in blender and blend for 20 seconds.
Add melted gelatin, salt, radish sprouts and mayonnaise.
Blend 10 seconds.
Turn out into bowl and fold in whipped cream.
Pour into quart mold and chill several hours.
Unmold onto platter and garnish with watercress.