 Complete the following phrase:  The University of Helsinki Botanical Garden has its roots in the Imperial Academy of Turku Botanical Garden, which was established by Professor Elias Tillandz in 1678. Tillandz garden was a small garden for growing cabbages and medicinal plants. After Tillandz death, the garden was left to its own demise until Professor Pehr Kalm took responsibility for it. The garden started to flourish as Kalm brought hundreds of useful plants with him from North America. When the Imperial Academy of Turku relocated to Helsinki in 1828, it was allocated a piece of land in Kaisaniemi that had previously served as common pasture for the people of Helsinki. Professor of Zoology and Botany Carl Reinhold Sahlberg started construction on a new garden, relying on his extensive private collection that was not destroyed in the 