138 ANATOMY. 



membranes may be united and confounded, so as to become indistinct. The primine 

 therefore cannot be identified with the testa, except in cases when the latter can be 

 cleanly removed, exposing the raphe between it and the endopleura ; and then the 

 endopleura is obviously formed by the secundine, with or without the tercine and 

 quintine, as may be easily seen in the Orange. 



The three typical modifications in the positions of the parts of the ovule being 

 known, we will indicate the corresponding portions of the embryo in the seed : — 



First Type. — Ovule straight (ortJwtropous), and consequently embryo antitropous ; 

 — the seed may be: 1, erect (radicle superior) ; 2, pendulous (radicle inferior) ; 3, hori- 

 zontal-parietal (radicle centrifugal) ; 4, horizontal- axile (radicle centrifugal). 



SECOiirD TrPE. — Ovule reversed {anatropous), and embryo homotropous ;— the seed 

 may be : 1, erect (radicle inferior) ; 2, pendulous (radicle superior) ; 3, horizontal- 

 parietal (radicle centrifugal) ; 4, horizontal-axile (radicle centripetal). 



Third Type. — OrxAe curved {cawpylotropous), and embryo amphitropows ; if the 

 embryo is not much curved, the radicle is inferior, superior, centripetal, or centri- 

 fugal, according to the position of the micropyle ; if neither extremity of the embryo 

 is turned towards the hilum, owing to the unequal growth of the coats, it is said to 

 be heterotropous ; it may then be either straight, curved, or flexuous, and the radicle 

 is inferior, superior, centripetal, centrifugal, or vague. 



ACCESSORY ORGANS. 



To complete the anatomy of the elementary and fundamental organs, we must 

 describe that of certain modifications of the cellular tissue : these are prickles, hairs, 

 (jlands, and lenticels. 



Prickles. — These are composed of a cellular tissfue analogous to that of the hark; 

 they must not be confounded with spines, which are fibro-vascular, and are merely 

 transformed organs, whose nature is indicated by their position; i.e. they are 

 aborted branches {Blackthorn, fig. 51), hardened stipules {Rohinia, fig. 114), petioles of 

 pinnate leaves become spiny after the fall of the leaflets {Astragalus Tragacantha), 

 leaves of which the nerves have lengthened into spiny points, to the destruction of 

 the parenchyma {Berheris, fig. 94) ; cushions, which elongate greatly, and become 

 pungent {Gooseberry, fig. 95). Prickles, on the contrary, are dispersed without order 

 on the stem and leaves, and even on the corolla, and are thickened, hardened, and 

 pungent hairs. When young, they exactly resemble hairs, of which we 

 are about to speak, and it is only when older that they thicken, 

 lengthen, and harden ; they occur on the Rose (fig. 50) in every stage 

 of its growth. 



Hairs. — Cellular organs, which principally occur on branches, 



731. Cabbage. petiolcs, and the nerves and under surface of leaves, especially young 



^'^ll^Tmi'f''^ °"^^ ' ^^^^ ^^^ lengthened epidermal cells, covered by cuticle, like 



those cells which do not lengthen. Hairs are unicellular, when formed 



of one elongated, vertical, oblique, or horizontal cell, which may remain simple 



