CHAP. I.] 



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 first, 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 The upper flowers are pis- 

 illustrated by turnips and car- tillate or female, the lower 

 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. 



large catkins staminate or 

 male. 



