SEEDS AND SEEDLINGS 



17 



simplest structure throughout (Fig. 4). Floating through 

 the air like chaff, they are borne to situations suited to 

 the life habit of these plants. The very much reduced 

 embryo is a minute rounded body with no sign of leaf 

 and stem appearing until germination has considerably 

 advanced. 



5. But every well-developed embryo consists essentially 

 of a nascent axis, or stem, the caulicle, bearing at one 

 end a leaf or leaves, the cotyledons, while from the 

 other end a root is normally to be produced (Fig. 3, d). 



6. The number of cotyledons. Several of the embryos 

 examined in the laboratory were dicotyledonous, that is, 

 two-cotyledoned. Plants which are thus similar in the 

 plan of the embryo, agree likewise in the general struc- 

 ture of their stems, leaves, and blossoms ; and thus form 

 a class, named from their cotyledons, 



the DICOTYLEDONS. 



7. Figure 5 represents the Pine seed 

 seen in section, together with the young 

 tree after its cotyledons are fully ex- 

 panded. Of these there are several, a 

 case which is much less usual, but con- 

 stant in the various kinds of Pine, where 

 in some species the cotyledons number 

 twelve, or even more. And in some 

 other Coniferce, or cone-bearing trees, 

 the same peculiarity is found. The em- 

 bryo is here said to be polycotyledonous. 



8. The term monocotyledonous denotes 

 the possession of but a single cotyle- 

 don. This condition goes along with 



other peculiarities of external and internal structure, and 

 is thus characteristic of a class of plants exemplified by 

 the true Lilies and the Grasses called the MONOCOTYLE- 

 DONS. 



9. In addition to the parts already referred to, many 

 embryos show in miniature one or two lengths of the stem 

 which is to carry the growth of the plant upward above 



OUT. OF 3OT. 2 



5. Section of a Pine 

 seed; seedling 

 showing 6 coty- 

 ledons. 



