Development of ovule and testa of Linum usitatissimum L.

The ovule primordium of Linum usitatissimum is trizonate and both the outer and inner integument are of dermal derivation. The inner integument ultimately becomes about 14 cell layers thick, the inner layer is developed as an endothelium, and the middle layers bring about the ultimate shape of the ripe seed. The seed-coat is formed out of the outer integument and the outer and inner layers of the inner integument. The outer layer of the seed-coat consists of slime cells. In an aqueous medium slime diffuses from this layer through ruptures in the cuticle and forms a coat around the seed. The mechanical layers of the seed-coat consist of the fibrous cells of the exotegmen and of the cells of the endotegmen, which latter contain pigment and have pitted walls. The family of the Linaceae is assumed to be related to Geraniaceae, Oxalidaceae or Malpighiaceae.