OF THE EMBRYO AND SEEDLING. 13 



in the process of germination, and originates in tissue just back 

 of that which covers the root-end of the caulicle, and which, 

 being carried forward by the subjacent 

 formation (to which it becomes a sort of 

 cap or sheath) , is called the Root-cap. 

 As the primary root thus began b}' a 

 new and local growth at the extremity 

 of pre-existing stem, so it goes on to 

 grow in length wholly or mainly by a 

 continuation of this formation, the new 

 at the end of the old. That is, the 

 root elongates by continual minute 

 increment of its apex or near it, the 

 formed parts very soon ceasing to 

 lengthen. This is in marked distinc- 

 tion from stem, which grows by suc- 

 cessive individualized portions ; and 

 these portions (internodes) , at first 

 very short, attain or are capable of 

 attaining a considerable and sometimes 

 very great, but definitely terminable 

 length, by interstitial growth through- 

 out. Moreover, roots are naked, not 

 producing as they grow either leaves 

 or any organs homologous with leaves. 

 They commonly branch or divide, but 

 in a vague manner ; and their new parts bear what are called 

 Root-hairs, which greatly increase the absorbing surface ; other- 

 wise they are destitute of appendages or organs. 



25. With the Maple embryo, here taken as a type, that of 

 Morning Glory, Ipomoea purpurea, or any of its kin, may next 

 be compared. The cotyledons are different in shape, being as 

 broad as long, and notched both at base and apex. They lie 

 in contact in Fig. 14, and are ver} T thin, leaf-like, and green ~P 14- 

 while contained in the seed. Their thinness is shown in Fig. 13, T 14- 

 where a section of the crumpled and folded embryo, as it lies in 

 the seed, exactly divides them (passing through the terminal and 

 basal notches) and also the caulicle, which here is thicker than 

 both. The germination is similar to that of the Maple ; and like 

 that (as Fig. 16 shows), and for the same reason, no bud or ~P /4 

 rudiment of the further growth pre-exists in the embryo or 



FIG. 12. Red Maple seedling, with three joints of stem and pairs of leaves developed, 

 the first being the cotyledons. 



