EXOGENS. 



(i 188 \ II. EXOGfcNS. 



Dfcoj 



■ 



- bophyta, - 



Bi common consent the plants to which botan 

 of Dicotyledons, and which now bear that of I. 

 most completely formed of all the Vegetable Kingdom. Id the 



uised species thej possess a degree of vitality unknowi 

 Gymnogens. A century or two terminates the life of an Endo 

 unless in a few ran- cases; while many Exogens may bai 

 monarchs of their forests even at the comm it of tin- Christian 



This arises from their peculiar manner <>t' growth, which . 

 tion '>t' their vigour with each succeeding year : and it is in a!. 

 circumstance that their name has been contrived. 



K.\ogen9, or outward growers, an' jo called bi 

 tinue to grow they add new wood to the outside of that formed in I 

 rious year ; in which respect they differ essentially from Endi 



w 1 is constructed by successive augmentations from tin- in-. 



of cold climates, and the principal part of thosi in hot latitu 

 exogenous, In an I of ordinary structure tin- emb 



cellular mass, in which there is usually no trace of « ly or 



hut as - i as germination commences fine ligneous 



ing from the cotyledons toward- the radicle meeting in the centi 

 embryo, and forming a thread-like axis for the root. A- th< 

 ligneous cords are increased in thickness and number, and ha- n in- 



troduced among the cellular mass of the embryo, ai 

 other by a portion of the cellular substance, which contin 



both in length and breadth as the w ly cords extend. Bj 



plumule or rudimentary Btem becon inised, and having 



little, tonus ii|„,ii it- surface one, two, or more true 

 expand into thin plates of cellular substance traversed by li." 

 vein- converging at the point of origin of the leave-. It 

 interior of the young planl Bin examined, it will 1* 



ligneous cords have been added from the base of the :• 

 cotyledons, where they have formed a junction with the I 

 served to thicken the woody matter developed upon tl 

 ligneous cords which proceed from the base of the ' 

 centre of the new stem, there forming a solid axis, hut p 



with the outside, and leave a -mall -; . i ellular I 



they themselves being collected into a hollow .. 



the middle until they reach that point where ti 



dons meet in order toform the solid centi 

 jroes on lengthening and forming new lea> 



traced a formation of woody matter disp 



uniting with that previously formed : a cylind 



always left in the middle." The solid 



in its growth in a corresponding ratio, lengl 



and increasing in diameter a- the leaves unfold 



produced. The result of this i-, that wl 



at the end of it- first vear's growth it has 



