2i62 A TEXTBOOK OF THEORETICAL BOTANY 



primitive simply because certain whorls of floral parts are absent. Rather 

 it is thought that these parts, being unnecessary in flowers which rely on 

 wind for pollination, have been reduced and finally in some instances lost. 

 Hence the Apetalae are now regarded by many as reduced rather than 

 primitive families, originating from a polypetalous stock. The Rosales and 

 particularly the Hamamelidaceae have been suggested as a possible origin 

 of some of them, though it is recognized that the group is probably not a 

 natural one and contains families reduced from different ancestral types. 



Hutchinson in his treatment further elaborates the system by consider- 

 ing that the primitive polypetalous forms diverged from the start along 

 two separate lines, the one retaining the treelike habit of the ancestral 

 type, the other adopting an herbaceous habit. Thus he separates the 

 Magnoliales as the first order of the arboreal types and retains the Ranales 

 for the related herbaceous families. He considers further that the apetalous 

 families have been derived partly through the Magnoliales and partly 

 through the Ranales. 



It is interesting to note that in the course of time the number of recog- 

 nized orders and families of Flowering Plants has increased, mostly due to 

 rearrangements and to some extent to new discoveries. In the " Genera 

 Plantarum " 200 families are recognized; * in the " Pflanzenfamilien " 280 

 families are described, while Hutchinson employed 332 families. The same 

 is true of the orders, of which Hutchinson has increased the number very 

 considerably. 



Some confusion of ideas has arisen about the implication of the term 

 Order as used by difl'erent writers on Angiosperm systematics. Bentham and 

 Hooker use the Linnaean term " Natural Order " for a collection of genera 

 and the term " Cohort " for a group of Natural Orders. Engler and most 

 modern writers adopt the term Family for Natural Order and the term 

 Order to imply the same meaning as Cohort, in accordance with the 

 international Rules. 



It is impossible to give in full detail the three main systems of classifica- 

 tion now in common use, namely those of Engler, Bentham and Hooker, 

 and Hutchinson. In order, however, that the student may be able to use 

 books employing different systems and more particularly because most 

 British Floras follow Bentham and Hooker, an outline of the three systems 

 is appended. 



* This number includes three families of Gymnospermae — Gnetaceae, Coniferae and 

 Cycadaceae — which were counted as Dicotyledons. English floristic writers following Bentham 

 and Hooker have continued this practice until recent times. 



