When the tuber of a potato begins to germinate the shoots which it puts out derive their food from the accumulated store of nutritive material which has been laid up in the cells of the tuber.
They soon acquire a cell-wall, and germinate without a period of rest.
Aplanospores would seem to represent zoospores arrested in their development; without reaching the stage of motility, they germinate within the sporangium.
Allowing for those which fail to germinate (perhaps 25%), loss in transplanting, weak and backward plants, &c., one ounce of seed should yield about 40,000 plants.
The spores germinate on a damp surface and enter the cortex through small cracks or wounds in the protecting layer.