The Plant Modeler in Carrara can create very complex objects that take a lot of time and memory. If your system appear to freeze, just wait a couple minutes and you should be able to manipulate the program again. It is usually a good idea to keep the number of generations as low as possible since a high number of generations can create extremely complex trees. Some of the preset plants are more complex than others and may be too hard on older systems. Some of the slower plants include Beech, Bur Oak and Christmas.