SEED. 



Ill 



whence the name Dicotyledons. Some species (Pines, fig. 620), possess six, nine, 

 and even fifteen whorled cotyledons. 



Other phsenogamic plants have only one cotyledon ; whence the name Mono- 

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

 some Cruciferw, blue in Salpiglossis, green in the Spindle-tree and Maples, and pink 

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

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

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

 without a limb ; 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 



652. Bindweed. 



631. Mallow. Embryo spread 

 Embryo (mag.). out (mag.). 



633. Wallflower. 



Transverse section 



of seed (mag.). 



634. Rocket. 



Transverse section 



of seed (mag.). 



; and living on 

 plant, like the 



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

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

 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, *>r 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. accumbentes, 

 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, Rocket, 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 A Imond frequently pre- 

 sents two superimposed embryos, one of which appears to proceed 

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

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

 two cotyledons can be plainly seen. 



The monocotyledonous embryo is usually cylindrio or ovoid ; to distinguish the 



T 



636. Orange. 



Germinating seed. T, 

 testa ; c, included cotyle- 

 dons ; PL, steins ; G, plan- 

 tules. 



