CHAP. 1. j 



PLANT ARCHITECTURE. 



25 



common to flowering plants in general. As already- 

 explained, the work done by an individual that com- 

 pletes the full cycle of life may be conveniently divided 

 into two phases : first, vegetative ; second, re- 

 productive. In many of the lower types of 

 plant life, as already illustrated by the species of 

 Pleurococcus, these phases follow each other, the 

 first being completed before the second is en- 

 tered upon ; this condition also holds good in 

 numerous flowering plants — in fact, in all 

 annual species, or those that last for one season 

 only, and also in biennial species, 

 or those that live for two years 

 before completing the life-cycle. 

 The annual species develop the 

 vegetative portion flrst, this is 

 followed by the reproductive 

 during the same season, the last 

 phase producing seed that pro- 

 duces new individuals the fol- 

 lowing year. In biennials, the 

 first year is devoted entirely to 

 the vegetative phase, which 

 often concentrates a considerable 

 amount of reserve material or 

 surplus food in the root, as 

 illustrated by turnips and car- 

 rots ; during the second season 

 this reserve material serves to 

 build up the reproductive structure, consisting of a 

 stem bearing flowers, that in due course produce seed, 

 thus completing the life-cycle of the individual. A 



Fig. 4. A flower-bear- 

 ing branch, of the common 

 hazel {Corylus avellana), 

 a wind-fertilized flower. 

 The upper flowers are pis- 

 tillate or female, the lower 

 large catkins staminate or 

 male. 



