66 STRUCTURAL AND PHYSIOLOGICAL BOTANY. 



the advance of the embryo to maturity ; but it sometimes 

 remains surrounding the ripe embryo, in the form of Vitellus ; 

 Ex. Saururus, Piper 297 .- 



558. The embryo consists of the cotyledons (559), the 

 radicle (561), the plumule (560), and the collar (562). 



559. The cotyledons represent undeveloped leaves 295 ". 



560. The plumule, or gemmule, is the nascent ascending 

 axis (64) 2956 . 



561. The radicle is the rudiment of the descending axis 

 (7l) 295c . 



562. The collar is the line of separation between the radicle 

 and the cotyledons. 



563. The space that intervenes between the collar and the 

 base of the cotyledons is called the cauliculus. (Tigelle, Fr.) 



564. In some seeds the embryo is furnished with a 

 suspensor from the point of the radicle 300 . 



565. The embryo is usually solitary in the seed, but occa- 

 sionally there are two or several (472). 



566. When several embryos are produced within a single 

 seed, it sometimes happens that two of these embryos grow 

 together, in' which case a production analogous to animal 

 dicephalous monsters is formed. 



In form, position, and direction, the embryo varies in different species. In 

 general it is straight ; in some it is spiral 291 ; in others heliacal 294 ; in others 

 vermicular 290 ; in others arcuate 301 . It usually occupies the axis of the 

 albumen or seed 278 293 : but it is also excentrical 292 ; and unilateral 299 . In 

 direction, it is either erect with respect to the seed, or inverted or transverse. 



