t 





I 



142 MISSOURI BOTANICAL GARDEN, 



condition in the protoplasm. The walls react blue to iodine. The 

 small quantity of oil becomes more evident in the inner cells as drop- 

 lets removed from the protoplasm. — Zone b-b' . Thin-walled endos- 

 perm cells in which cell divisions occur, more especially in the layer 

 of cells between b and b' . Tension zone, contributing cells to zone 

 a' and to zone c. — Zone c. Endosperm in which the thickening of the 

 cell walls has progressed. The limit between zone 6 and zone c is 

 not a sharp one. (Zone c r is not visible, but has begun in the interior 

 of the endosperm, cf. fig. 26a.)— Zone b' now becomes compressed 

 between the advancing thickening endosperm, zone c. 



Figs. 16, 17 and 18.— Zone a. Cell walls entirely collapsed, reacting 

 blue with iodine. All the contents except minute droplets of oil have 

 entirely disappeared.— Zone a'. Cell walls not collapsed, reacting 

 blue with iodine. The cells nearer the embryo have no other content 

 that each a single large droplet of oil. The outermost have more or 

 less protein content. — Zone 6. Unaltered endosperm cells, the inner of 

 which are subject to digestion. The outermost cells of this layer are 

 represented by zone &'.— The tension zone becomes narrowed down to 

 zone 6', of cells undergoing division, and shearing between the grow- 

 ing endosperm and zone b.— Zone c. Endosperm with thickening cell 

 walls, giving a tannin reaction only in the lumen. Zone c'. Definitively 

 thickened endosperm cell walls. Deep tannin reaction in the eel- 

 walls in the younger stages but disappearing in the older ones.— The 

 zones now become compressed and the distinctions less marked or 

 nearly obliterated. 



Figure 19. — Zone a. Crushed and compressed cells reacting blue 

 walls and contents. This zone is separable into two zones by the 

 successful application of iodine and sulfuric acid. This treatment 

 produces a deep blue reaction which quickly fades away, and causes 

 swelling and dissolution. These proceed differently however in the 

 two layers a and a' figure 20. The compressed cell walls of layer a 

 swell and dissolve as a whole; those of a' first expand and assume 

 their original form previous to swelling, indicating that they are not 

 so far disorganized by digestion as those of a. The compressed cells 

 contain numerous minute oil droplets; the less compressed (a', f. 20) 

 large droplets.— Zone &'. Tension zone. The cells are partially thick- 

 ened, less toward the embryo, more toward the outside. They are 

 secondarily divided by transverse walls. They contain protoplasm 

 and oil, the latter in large drops, the protoplasm more or less dis- 

 organized. — Zone c. Definitively thickened and characteristic endos- 

 perm cells. 



It may here be noted that the distribution of oil in the compressed 

 zones is not as figured by Sachs (his figure 4, pi. 9, 1862), who repre 

 sented large drops as occurring anywhere within the compressed layer. 

 The treatment with sulfuric acid demonstrates this very beautifully, 

 as the droplets are displayed in their relative positions as the wall 

 material swells. This is true of the whole period of germination. 



