The glassballs have adapted to the cold environment in the north tundra. To prevent being frozen, they evolved a shell around the main body. The shell doesn't touch the main body, but the space between these two is filled with air. Air is a heat isolator and helps the glassballs to prevent being frozen. Of course, the shell is composed of dead cells, so it can't grow. To grow, the main body has to extend, and this only happens when the environment is warm. So when it's warm (because of the sun for example), the main body will extend and touch the shell. Then the outer cells of the main body begin to harden, and the outer cells of the shell will be pushed outwards. When it will be colder, then the main part will contract to make use of the air filled space. During a very cold time, the glassballs can even release an anti-freezing compound into the cells, which prevents the growth of ice crystals and therefore the destruction of the cells. During this time, the cells are nearly inactive. This is quite similar to a hibernation. The shell is transparent and, due to the warping of sunlight, all light shining on the surface will be redirected to the inner main body. Its primitive roots collect water and nutrients, which are needed for photosynthesis. Although the glassballs reproduce asexually as their ancestors, they do it another way. They can't simply bud, because of the shell and the fact that the roots are too short, but they will produce mini versions of their own inside the shell. After they have reached the maximal size, the shell will lose the connection to the main body, which has already died off, and will be blown away by the wind, along with the mini glassballs.