248 Practical Plant Biology. 



As in the Buttercup the oosperm forms a cell-wall and by cell- 

 division produces a short column of cells lying in the micropylar 

 end of the embryo-sac (megagametophyte). From the two lowest 

 cells of this column the embryo is developed. The rest of the 

 column is the suspensor. By repeated divisions these two cells 

 give rise to an ovoid mass of cells. A shallow indentation on one 

 side divides the embryo into two lobes : that next the suspensor 

 develops into the root and the lowest part of the stem and that on 

 the other side of the indentation becomes the single seed-leaf 

 (cotyledon). Meanwhile the fusion-nucleus in the central region 

 of the ccenocytic megagametophyte divides and its products 

 divide again and again. The nuclei thus produced are distributed 

 in the augmenting cytoplasm. Later on cell-walls subdivide this 

 into cells each containing a single nucleus. The growing embryo 

 is embedded in the tissue (endosperm) so formed, which supplies it 

 with food. During these changes the small white ovule swells and 

 becomes a globular seed. The outer integument grows into a 

 black and shiny seed-coat. The syncarpous ovary also increases 

 greatly in size and becomes the fruit. Its wall dries and loses its 

 green colour, and when the seeds are ripe it cracks open and ex- 

 poses the shining black seeds within. The flowering stem by 

 this time is stiff and erect, and the flower-stalks which were before 

 pendulous now stand rigidly erect These changes secure that 

 when the flowering stem is pushed aside by a passing animal or by 

 a gust of wind it springs back into its vertical position ; but in so 

 doing it slings some of the seeds out of its open capsules. The 

 elasticity of the parts jerks them to considerable distances, and 

 thus disseminates them away from the parent. 



The seed is shed in the summer and lies dormant till next spring 

 when under normal conditions it germinates. The cotyledon 

 elongates and forces the young root out, thrusting it into the soil. 

 Immediately new roots are formed from the base of the stem and 

 fix the seedling in the soil. Just below the apex of the stem a new 

 leaf is formed, which develops chloroplasts and carries on photo- 

 synthesis. Till this function has been initiated, the cotyledon, still 

 retaining its top in the seed, continues to transfer nutriment to the 

 seedling. Once independent the cotyledon atrophies and con- 

 nection with the seed is severed. 



From this account it appears that the life-history of the wild 

 Hyacinth corresponds very completely with that of the Buttercup. 

 The herbaceous sporophyte is a complex, independent, holophytic 

 plant. In addition to its vegetative organs it produces sporophylls 

 which are grouped together on shortened axes to form flowers. 



