384 A TEXTBOOK OF BOTANY [Cn. VIII, 4 



Sixth, the parts which rise in the light, especially the 

 cotyledons and plumule, as they issue from the seed coats, 

 begin to turn green, and, by the time they are spread open 

 at the top of the young stem, have their full quota of chloro- 

 phyll, in obvious preparation for the manufacture of new 

 food. 



Seventh, the enlargement of hypocotyl, cotyledons, and 

 plumule proceeds by absorption of water until all of the 

 cells laid down in the embryo are fully expanded, at which 

 time, with the root firmly fixed in the ground, the young 

 stem is erect with the cotyledons fully green and expanded. 

 Germination is now complete, and the germinated embryo 

 is ready to continue development, with formation of new 

 parts, into a seedling. It is true, the formation of new 

 leaves and buds does not always await the completion of 

 the expansion of embryonic parts, but in principle at least 

 there is this distinction between germination and the sub- 

 sequent growth of the seedling. 



If a fully germinated embryo be compared point by 

 point with one from a resting seed, as may best be done with 

 some of the compact succulent kinds like Cactus, the fol- 

 lowing differences appear. First, except for the root and the 

 chlorophyll, the germinated embryo possesses nothing really 

 new. Second, it has become many times larger, even to 

 twenty or thirty times. Third, again excepting the root, it 

 has usually few new cells, the enlargement having consisted 

 chiefly in the increase in size of those already developed. 

 Fourth, the cells are now all apparently empty (except for 

 water) instead of densely packed with solid food, thus 

 explaining the watery translucency of the germinated 

 embryo as contrasted with the white opacity of its unger- 

 minated condition. Fifth, its dry weight, determined by 

 comparative weighings of oven-dried material, is actually 

 less, showing that the far greater bulk consists chiefly of 

 water. Thus it is clear that germination consists primarily 

 in the great expansion through water absorption of the 



