SEED-BEARING PLANTS 



391 



having prominent midribs and pinnately divided (Fig. 

 285). The leaves endure for a year or more (varying 

 with the species), and are then replaced by a fresh crown. 

 The duration of each crop of leaves is said to vary accord- 

 ing as the plant grows wild,- or in botanic gardens and 



Fig. 286. — Cycas revolula. , Terminal bud of foliage leaves just opening. 

 Nearer view of Fig. 285. Note the circinate vernation of the leaf-pinnules, 

 but not of the entire leaf. 



conservatories. Thus, when temperature and rainfall are 

 excessive, Cycas circinalis may produce two crowns of 

 leaves a year, instead of the one crown commonly produced 

 in green houses. 



The young leaves are curled up at the tips, unrolling 

 as they grow. In the genus Cycas only the leaflets are 



