INTR OD UCT1ON xi 



species in the genus, and its geographical distribution. The number, 

 unless very small, is always only an approximation ; new research is 

 always bringing new species to light, splitting up older ones, or com- 

 bining two or more into one. This is all the information that is given 

 about a very large number of the genera ; only when a genus presents 

 some character of interest which is not common ta the order or group, 

 is any particular mention made of it. The biological peculiarities of the 

 most important genera are dealt with pretty fully, but much has been 

 omitted. Thus in dealing with the pollination-methods of flowers a 

 selection of important genera, illustrating the various methods, has been 

 made for description ; so too with epiphytes, xerophytes, the morphology 

 of parts, and so on. General discussions of all these subjects will be 

 found under the title of the subject itself, and numerous examples are there 

 quoted; these examples are mostly dealt with more fully. Numerous 

 cross-references to other articles, e.g. Buds, Dichogamy, Fruit, Leaf, 

 Parasite, Xerophyte, &c. (cf. Index), are made, and should be looked up. 



While in the morphology, &c. a selection has thus been made of 

 genera for treatment, this is less the case with economic botany. This 

 has been more fully treated, only a comparatively few genera being 

 omitted. Space, however, has not permitted of a detailed description of 

 economic products or the way in which they are obtained ; for this 

 reference must be made to other works (see Literature). 



Turning now to the other articles upon the families, the same general 

 principles apply to them. After the name of the family is given the 

 order to which it belongs, marked EP. or BH. if necessary to distinguish 

 between these systematists. This should be looked up in the key at the 

 end ; this will show the families which are most nearly related to the 

 one under consideration, and the characters that distinguish one from 

 the other can be made out by comparison of their descriptions. The 

 student should always endeavour to make out why a given family is 

 classified in the position assigned to it. When the family as defined by 

 Engler differs from that defined by Bentham and Hooker, as is so often 

 the case, an attempt should be made to discover the reasons for the 

 difference. 



After the position of the family in the system follows the number of 

 its genera and species, the morphology and natural history of its vegeta- 

 tive and reproductive organs, its economic products, and finally, in the 

 case of the more important families, its classification into sub-families 

 and tribes, with the more important genera belonging to each. The 

 student should work through this part and study as many of the genera 



