16 



MORPHOLOGY OF THE SEEDLING 



The root hairs in plants growing under ordinary conditions 

 are surrounded by the moist soil and wrap themselves around 

 microscopical particles of earth (Fig. 9). Thus they are able rap- 

 idly to absorb through their thin walls the soil water, with what- 

 ever mineral substances it has dissolved in it. 



23. The young stem. The hypocotyl, or portion of the stem 

 which lies below the cotyledons, is the earliest formed portion 



FIG. 9 

 FIG. 9. Cross section of a root 



FIG. 10 



A good deal magnified, showing root hairs attached to particles of soil, and some- 

 times enwrapping these particles. After Frank and Tschirch 



FIG. 10. A turnip seedling, with the cotyledons developed into 

 temporary leaves 



h, root hairs from the primary root ; b, bare portion of the root, on which no hairs 

 have as yet been produced 



of the stem. Sometimes this grows but little ; often, however, 

 the hypocotyl lengthens enough to raise the cotyledons well 

 above ground, as in Fig. 10. 



The later portions of the stem are considered to be divided 

 into successive sections called nodes (places at which a leaf, 

 or a scale which represents a leaf, appears) and internodes 

 (portions between the leaves). 



