SEED. 



Ill 



whence the name Dicotyledons. Some species {Pines, fig. 626), possess six, nine, 

 and even fifteen whorled cotyledons. 



Other phgenogamic plants have only one cotyledon ; vrhence the name Mono- 

 cotyledons. The colour of the embryo varies ; it is white in most plants, yellow in 

 some GrucifercB, blue in Salpiglossis^ green in the 8pindle-tree and Maples, and pinle 

 in Thalia. The cotyledons are generally fleshy, their parenchyma is oily in the 

 Walmit and the Almond, and mealy in the Kidney-bean ; they have sometimes dis- 

 tinct nerves {Berberis, fig. 627) 5 they are sessile or petioled, or reduced to a petiole 

 without a limh ; this is especially the case in monocotyledons. They are usually 

 entire and equal, but may be lobed [Geranium, Walnut, fig. 628), or palmate [Lime, 

 fig. 629), or very unequal, with the smaller so minute that the plant might be mis- 

 taken for a monocotyledon (Trapa). Those of the Nasturtium and Horse-chestnut- 

 unite as they grow old into a compact mass. In some 

 parasites they entirely disappear, and the embryo is reduced 

 to its axis ; as in Cuscuta (fig. 630), whose thread-like stem 



is attached to the plants it preys on, by suckers (p. 16, fig. 48) ; and living on 



their juices, it needs no leaves to elaborate sap; and the adult plant, like the 



embryo, possesses no leaves. Cotyledons are sometimes folded in 



halves, along their median line ; or convolute [Mallow, fig. 631) ; 



or spiral [Hop) ; or crumpled [Bindweed, fig. 632) ; the embryo 



itself is straight, or curved, or zigzag, or annular, or spiral, or 



rolled into a ball, &c. Often the radicle is turned up on the 



cotyledons ; if it is then placed against their commissure it is said 



to be lateral, and the cotyledons are accumbent [c. accwmbentes. 



Wallflower, fig. 633) ; if it is on the back of one of the cotyledons, 



it is said to be dorsal, and the cotyledons are incumbent (c. 



incumbentes. Rochet, fig. 634). 



Some seeds contain several embryos ; the Orange (fig. 635) has 

 often two, three, or four unequal, irregular, and convolute, the 

 cotyledonary ends of all facing the chalaza, and their radicles 

 facing the micropyle ; they all leave the seed at the period of 

 germination (fig. 636). The seed of the ^ZmomcZ frequently pre- 

 sents two superimposed embryos, one of which appears to proceed 

 from the first, like successive internodes (fig. 637) ; they may be 

 easily separated (fig. 638), when their respective radicles and 

 two cotyledons can be plainly seen. _ - ■. +v 



The monocotyledonous embryo is usually cylindri'5 or ovoid ; to distinguish the 



63G. Orange. 

 Germinating seed. T, 

 testa ; c, inclnded cotyle- 

 dons ; PL, stems ; a, plan- 

 tules. 



