10 



GROWTH AND WORK OF PLANTS 



(see fig. 1 6). They are really adventitious roots since they arise 

 from the stem. The true lateral roots arise from the primary 

 root and extend in a nearly horizontal direction, and the branch- 

 ing of these finally results in a great mass of fibrous roots radiat- 

 ing in all directions in the upper soil layers. About the same 

 time or very soon after the root emerges, the conical fold of the 

 leaves emerges from the other end of the groove. This conical 

 form of the folded leaves wedges its way directly upward through 

 the soil. The leaves elongate and unfold. 



THE PINE. 



13. The pine seed. The seeds of the pine are formed on 

 the upper (inner) surface of the scales of the pine cone (see 

 paragraph 529 on cones of the pine). The seeds 

 are oval and somewhat compressed and flattened, 

 sc and attached to the lower end of the scale, two 

 on each scale. As they become freed from the 

 .end scale a long, thin and broad strip of the scale 

 splits off and remains attached to the seed as 

 a wing. A section of the seed shows the thin 

 'section P a P erv remnant of the nucellus lying between the 

 of. sc. seed coat; n, see( j coa ts and the white mass of the endosperm. 



remains of nucellus; 



end. endosperm (= Within this lies the embryo. The root and stern 



female gametophyte); ' 



form a 



c y lindri - 



P n y te - . cal portion, and 



at the stem end there is a crown 

 of small needlelike leaves, the seed 

 leaves or cotyledons. The cotyle- 

 dons are numerous in the pines. 

 The embryo is entirely destitute of 



, j . . 



chlorophyll, but during germma- Embryo of white 



tion, even if the seedlings are grown S t JSJS2 



in the dark the leaves become cotyledons. 



green. In germination the radicle emerges from the micropylar 



end of the seed. The hypocotyl elongates and forms a loop which 



pulls the leafy end of the stem and the cotyledons from the ground. 



Fig. 19. 



9* 



Fig. 20. 



Pine seedling just 

 from the 



