SECTION 



3.J 



SEEDLINGS. 



23 



constructed upon one and the same plan, namely, that of two leaves on a 

 caulicle or initial stem, — a plan which is obvious even when one cotyledon 

 becomes very much smaller than the other, as in the rare instance of Abro- 

 nia (Fig. 54, 55). Im other words, the embryos so far examined are all 



37. Dicotyledonous, that is, two-eotyledoned. Plants which are thus 

 similar in the plan of the embryo agree likewise in the 'eneral structure of 



46 48 60 



their stems, leaves, and blossoms ; and thus form a class, named from their 

 embryo Dicotyledones, or in English, Dicotyledonous Plants. So long 

 a name being inconvenient, it may be shortened into Dicottls. 



38. Polycotyledonous is a name employed for the less usual case in 

 which there are more than two cotyledons. The Pine is the most familiar 

 case. This occurs in all Pines, the number of cotyledons varying from three 

 to twelve ; in Pig. 56, 57 they are six. Note that they are all on the same 

 level, that is, belong to the same node, so as to form a circle or whorl at the 

 summit of the caulicle. When there are only three cotyledons, they divide 

 the space equally, are one third of the circle apart. When only two they 

 are 180° apart, that is, are opposite. 



39. The case of three or more cotyledons, which is constant in Pines 

 and in some of their relatives (but not in all of them), is occasional among 

 Dicotyls. And the polycotyledonous is only a variation of the dicotyledonous 

 type, — a difference in the number of leaves in the whorl ; for a pair is a 

 whorl reduced to two members. Some suppose that there are really only 



Fio. 46. Section of a seed of a Peony, showing a very small embryo in the 

 albumen, near one end. 47. This embryo detached, and more magnified. 



Pig. 48. Section of a seed of Barberry, showing the straight embryo in the 

 middle of the albumen. 49. Its embryo detached. 



Piq. 50. Section of a Potato-seed, showing the embryo coiled in the albumen. 

 51. Its embryo detached. 



Flo. 52. Section of the seed of Mirabilis or Four-o'clock, showing the embryo 

 coiled round the outside of the albumen. 53. Embryo detached; showing the very 

 broad and leaf-like cotyledons, applied face to face, and the pair incurved. 



Flo. 54. Embryo of Abronia umbellata; one of the cotyledons very small. 

 55. Same straightened out. 



