THE PAKTS OF THE SEEDLING. 



15 



called water-hyacinth' that which occupies the place of an 

 ordinary root-cap is a long sheath, which may be pulled off 

 entire ; its large size is possibly due to the fact that it is not 

 worn away by friction against the soil. 



19. The Young Stem. — The caulicle, or portion of the 

 stem which lies below the cotyledons, is the earliest-formed 

 portion of the stem. Sometimes 

 this lengthens but little ; often, 

 however, as the student knows 

 from his own observations, the 

 caulicle lengthens enough to 

 raise the cotyledons well above 

 ground, as in Fig. 5. 



The later portions of the stem 

 are considered to be divided into 

 successive nodes, places at which 

 a leaf (or a scale which repre- 

 sents a leaf) appears, and inter- 

 nodes, portions between the 

 leaves. 



The student should watch the 

 growth of a seedling bean or pea 

 and ascertain by actual measure- 

 ments whether the internodes 

 lengthen after they have once 

 been formed, and if so, for how 

 long a time the increase con- 

 tinues. Kg. 5. — I, a seedling maple, natural 



, size ; c, cotyledons ; d, plumule ; o, 



The rate of growth may readily be ^^^^^ „{ jj^e ground ; n, part of root 

 measured hy means of a simple piece of the same, magnified six times, 

 of apparatus, shown in Fig. i. This stowing root-hairs, 

 consists of a pointer L supported hy 

 an upright stand, moving over a graduated arc, and with a grooved 



•■ A plant somewhat common in greenhouses, alUed to the ordinary pickerel weed 

 of the streams and ponds of New England. 



