THE PARTS 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 cauliele, 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 

 cauliele 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. 



Fig. 5. — I, a seedling maple, natural 

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

 level of the ground ; II, part of root 

 of the same, magnified six times, 

 showing root-hairs. 



The rate of growth may readily be 

 measured by means of a simple piece 

 of apparatus, shown in Fig. 4. This 

 consists of a pointer i supported by 

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



1 A plant somewhat common in greenhouses, allied to the ordinary pickerel weed 

 of the streams and ponds of New England. 



