SPOKES. 59 



or, if two are present, one is minute or abortive. Such plants are also called 

 ENDOGENS (ej'J'ov, inside, ymfM-M, to originate or grow), because their stems increase 

 by internal accretions (197). Such are the grasses, the palms, the Liliacese, &c., 

 v.-hose leaves are mostly constructed with parallel veins. 



127. Dicotyledonous plants are such as bear seeds with two cotyledons. 

 These are also called exogens (sSa, outside), because their stems increase by 

 external accretions, including the bean tribe, the melon tribe, all our forest trees, 

 &e. These are also distinguished at a glance, by the structure of their leaves, 

 which are reticulate-vciued, that is, with veins dividing and uniting again, like 

 network. 



FIG. 19. — Structure of seeds and germination; 1, seed of a garden bean; 2, the same 

 after ^ermijiation is commenced and the skin llirown ofi'; .3, seed of Triglocliin (magnified) ; 

 a, fungous clialaza, b. raplie, c, hilum; 4, embryo ; a, cotyledon, 6, radicle, c, fissure, beneath 

 which lies the plumule; 5, vertical section of the same; rf, ihe radicle seen beneath the 

 fissure ; 6, germinating seed of Alisma ; a, cotyledon, 6, plumule, c, radicle ; 7. seed of Canna 

 lulea, vertical section, a, albumen, ft, emliryo ; S, fruit of Mirabilis, showing the cotnmence- 

 ment of germination, the embryo protruding the radicle ; 9, the same, having thrown ofi" ihe 

 pericarp and become a young plant; 10, germinating seed of Calla .^thiopica ; a, seed, 6, 

 first leaf of plumule, r, radicle ; 11, section of the fruit of a grass with the embryo at base; 

 12, the same aficr germination lias commenced ; 13, the germination completed, and the 

 young plant formed; 14, embryo of Pinus, showing the numerous cotyledons; 15, the same 

 after germination has commenced ; 16, embryo of Cuscuta, having no cotyledon. 



128. The pine and fir have seeds with from two to throe cotyledons, while the 

 dodder (Cuscuta) is almost the only example known of an embryo with no coty- 

 ledon. 



129. A few plants, as the onion, orange, ConiferiS, &c., occasionally have two 

 or even several embryos in a seed, while all the Ckyptogamia, or flowerless 

 plants, have no embryo at all, nor even seeds, but are reproduced from spokes, 

 (48) bodies analogous to the pollen grains of flowering plants. 



