106 FUNCTIONS OF THE ROOT AND LEAVES ORIGIN OF WOOD. 



and others none. These apparent variations have been suf* 

 ficient to induce some Botanists to reject entirely this classi- 

 fication, hut we believe on very insufficient grounds, since by 

 careful observation nearly all these apparent discrepancies 

 may be reduced to a common principle ; and even if they 

 could not be explained at all, the foundation of the system 

 would be broader and firmer than any other proposed by the 

 objectors to this. Could v/e expect that the many thousand 

 different species of vegetables varying almost infinitely in 

 their various parts could be reduced to three actual, invariable 

 types? It would be requiring of this system what has nev- 

 er been attained in any other. 



127. Orders in which more than two cotyledons arc found 

 are the Coniferse, in which they vary in number from two to 

 more than twelve ; in Boragineae and Brassicaccae and some 

 other orders there are four. In all these cases the cotyledons 

 are opposite. In the iJorse-chestnut, there is apparently but 

 one cotyledon. Prof. Lindley says, that'by dissection there 

 is a Slit which indicates the division between the two bases 

 of a n;iir of opposite confluent cotyledons. Some such mod- 

 ification doubtless is the cause of all the variations from the 

 common type. 



128 Thereareother cases in which no cotvledons exist. The 

 Cuscuta is an example of this kind, but if the cotyledons are 

 leaves, we should not expect to find cotvledons in this genus, 

 since it has no leaves. There are other cases in whicii it is 

 said no cotyledons are discernable, but by more accurate ob- 

 servation 'the cotyledons are found to exist in a rudimentary 

 state, the radicle seeming to be developed at their expense. 



The monocotyledonous embryo is very different in its 

 structure from {he preceding. It is a homo^feneous, cvlindrical 

 body, tapering at both ends, with no distinction of radicle, 

 plumula or cotyledon. 



CHAPTER IV. 



FUNCTIONS OF THE ROOT AND LEAVES ORIGIN OF WOOD. 



129. In the preceding chapters we have described the vari- 

 ous organs which compose the vegetable in its most perfect state, 

 but we have considered them, with few exceptions, simply as 

 they present themselves to the eye, without supposing them 

 possessed of life, or considering them in their combined action 



