SPORES. 



59 



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

 ENDOGEXS ((vifov, inside, ■}ivo/aui, to originate or grow), because their stems increase 

 by internal accretions (197). Sucli are the grasses, the palms, the Liliacca;, &c., 

 whose leaves are mostly constructed with parallel veins. 



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

 These are also called exogexs (ua, outside), because their stems increase by 

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

 &c. Tliese are also distinguished at a glance, by the structure of their leaves, 

 which arc reticulate-veined, that is, with veins dividing and uniting again, like 

 network. 



v^ a^^ r^ /^5 



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

 after germination is commenced and the skin thrown off; 3, seed of Triglochin (magnified) ; 

 n, fungons chalaza, t, raphe, c, Inlum ; 4, embryo ; a, cotyledon, 6, radicle, c, fissure, beneath 

 which lies the plumule ; 5, vertical section of the same ; <i, the radicle seen beneath ilia 

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

 lutea, vertical section, a, albumen, 6, embryo ; 8, fruit of Mirabilis, showing the commence- 

 ment of germination, the embryo protruding the radicle ; 9, the same, having thrown off the 

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

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

 12, the same after germination has 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 >vith no coty- 

 ledon. 



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

 or even several embr}-os in a seed, while all the Crtptogamia, or flowerless 

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

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



