Centuries before the time of Christ, Egyptian records show that plants were being grown in the Nile without the use of soil and Marco Polo describes floating gardens in China in the thirteenth century. Over the past one hundred and fifty years, a great deal of research has taken place into soil-less cultivation, particularly during and after the Second World War when there was a need to produce food for military personnel stationed in areas where it would be otherwise impossible to raise fresh produce. Nowadays, in so-called developed countries, a great many plants are produced hydroponically. In Europe, for instance, around 80% of tomatoes and 90% of cucumbers come from hydroponic systems, as does much of the huge production of flowers in Holland.