Physiological dormancy comes in three types with each of them having their own characteristics.
Non deep Physiological dormancy
The first being the non deep dormancy. This dormancy is an easy dormancy. It requires a very little period of prechilling to break the dormancy barrier. Germination will occur at temperature above 15 Celsius degrees. Light can be a factor in germination. Some known chemical compounds, like ga3, can help and improve the germination of tree seeds with a non deep physiological dormancy.
Intermediate Physiological dormancy
The second being the intermediate dormancy. The period of dormancy and prechilling required for this type of seeds is a bit longer then non deep dormancy seeds. Anywhere from 1 to 6 months could be required the break dormancy. An excised embryo will still grow and germinate eventually. Chemicals will also help germination for this type of tree seeds.
Deep Physiological dormancy
The third and last of physiological dormancy seeds is the deep dormancy tree seeds. Contrary to the intermediate dormancy, an excised embryo will grow. But, one exception exist, the prunes seeds are still growing after being excised even if they are considered a deep dormancy tree seeds. Deep dormancy type of seeds are requiring the longest period of dormancy period which is usually anything from 3 months to even 2 years. Some studies have shown that these type of seeds could have 2 levels of dormancy barrier.
This type of dormancy is usually absent from shrubs and is mostly found in a few temperate and almost all tropical species of trees. This is a nonexistent barrier compared to other type of dormancy. The embryo is just undeveloped and under ideal conditions it will complete is development and germinates.
This third dormancy type is a combination of the first two ones. The name is self-explanatory. As morphological, the embryo is undeveloped. It needs to develop itself to germinate, but before or at the same time, a dormancy barrier must be broken. The type of climate needed to broke the germination barrier is either moist, cold or warm. Again, non deep, intermediate and deep type of physiological dormancy can apply with this type of dormancy.