SPORES. 



59 



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

 EXDOGEXS {tvSov, inside, yivo/Aut, to originate or grow), because their stems increase 

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

 whose leaves are mostly constructed with parallel veins. 



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

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

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

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

 which are reticulate-veined, 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 germination is commenced and the skin thrown off; 3, seed of Triglochin (magnified) ; 

 a, fungous chalaza, b, raphe, c, hilum ; 4, embrj'o ; a, cotyledon, 6, radicle, c, fissure, beneatli 

 which lies the plumule ; 5, vertical section of the same ; d, the 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, &, embryo ; 8, fruit of Mirabilis, showing the commence- 

 ment of germination, the embryo protruding the radicle ; 9, the same, ha\'ing 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. 



1 28. The pine and fir have seeds with from two to three cotyledons, while the 

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

 ledon. 



1 29. A few plants, as the onion, orange, Coniferte, &c., occasionally have tvvo 

 or even several embrj-os in a seed, while all the Cryptogamia, 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. 



6 



