NATURAL ORDERS. 91 



another on the other extreme. Some genera seem to 

 hold an intermediate place between two orders. 



3. The various species of the same genus are in the 

 same way allied, on one extreme, to one genus, and, on 

 the other, to another. 



Although there is an evident tendency to the above 

 conditions, yet they are not universally true. They 

 require to be very much modified, as follows : 



1. The relations, of genera particularly, in the series, 

 instead of being single and simple as above, are, in 

 many cases, compound and complicated. Thus a 

 plant is not only allied in certain .points to those which 

 are considered next to it, but it is related in other 

 points to various other plants, holding a place more 

 remote in the series. 



If we represent the series of relations by a chain, it 

 would not consist of single, simple links, but the links 

 in different parts, would be variously looped together. 



2. The series is variously interrupted ; in many in- 

 stances some links appear to he wanting. Many 

 plants are not connected at all and constitute solitary 

 links. 



Observation, Xaturalists have an opinion thai these deficiences 

 do not really exist in nature, but are occasioned by our partial 

 knowledge of the vegetable kingdom, This leads to the conclu- 

 sion, that a large portion of the vegetable world lies yet unexplor- 

 ed, and attaches additional importance to new discoveries. 



3. Some natural orders are strikingly marked, all 

 their genera being very similar among themselves, and 

 evidently distinct from all others, scarcely showing 

 any tendency to a gradual transition from one point to 

 another. Such are the Grasses, Umbelliferous plants, 

 and Compound flowers. 



4. Many genera are no less strikingly natural, the 

 species holding a very close affinity among themselves, 

 and differing essentially from all other genera, as the 

 genus Rose, and Violet. These are the most perfect 

 examples of genera. 



