SPORES. 



59 



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

 ENDOGEKS {tvSov, iusidc, yiv:fxii^ to Originate or grow), because their stems increase 

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

 whose leaves arc mostly constructed with parallel veins. 



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

 These are also called exogens (ela, 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, 6, raphe, c, hilum ; 4, embryo ; a, cotyledon, &, radicle, c, fissure, beneath 

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

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

 lutea, vertical section, a, albumen, 6, embryo ; 8, fruit of JMirabilis, 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 jEthiopica ; o, 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 three cotyledons, while the 

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

 ledon. 



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

 or even several embryos 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. 



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