58 EMBRYO. 



has been said against the division of plants into endor- 

 rhizte and exorrhiz<e, there can be no doubt of the 

 normal mode of the formation and protrusion of the 

 radicle as accompanying a mono, or dicotyledonous 

 embryo. 



312. In that class of plants called acotyledonous, the 

 nature of the embryo is that germination does not 

 ensue from two particular points of its structure, like 

 the plumula or radicle, but may do so from any part of 

 it : some of these plants, like the Ferns, however, pre- 

 sent other forms of structure, which rather entitle them 

 to go along with truly monocotyledonous plants, and 

 therefore the position of these tribes in the more general 

 divisions of systematology is at present doubtful : con- 

 cerning these plants, we refer to the systematical por- 

 tion of the work for an account of their more compound 

 organs. 



313. According to the position of the embryo in re- 

 lation to its coverings and their parts, it receives dif- 

 ferent terms. It is said to be antitropal when the ra- 

 dicle lies at the extremity of the seed farthest from the 

 hilum, as in the Nettle ; orthotropal, when the radicle 

 is at the end of the seed next the hilum, as in an Apple ; 

 heterotropal, when it lies cross ways, as in the Cowslip ; 

 and amphitropal, when the two extremities are pre- 

 sented to the hilum, as in the Dyer's-weed. Besides 

 these the cotyledons bear certain relations to the posi- 

 tion of the radicle, especially observed in cruciferous 

 plants ; when they have their edges presented to the 

 radicle, the terra cotyledons decumbent is used ; but when 

 the back of them is to the radicle, cotyledons incumbent. 

 But it has been shown by Kunth that these conditions 

 vary according to the age of the plant, as in Erysimum, 

 where they are at one time accumbcnt, and afterwards 

 incumbent. 



