426 BRITISH FLQWERING PLANTS chap. 



that it occurs in pulses. For some days, perhaps, no 

 flowers will be open ; then suddenly, without apparently 

 any change in the weather to account for it, the flowers 

 will all open together. This feature is especially marked 

 in the species which have single, or few flowers. For 

 wind -fertilised species the arrangement is obviously 

 advantageous. The flowers open once for all. 



There are 15 British species, mostly perennial. 

 Buchenau^ makes altogether 176, but many of these 

 vary considerably in certain districts, and he observes 

 that the more he studied these variations, the more 

 he was disposed to diminish the number of species. 



JUKCUS (Eush) 



J. articulatus. — Each flower lasts a day. It is female 

 in the morning, then hermaphrodite. The species is 

 supposed to flower in pulses. The leaves are hollow 

 and divided by partitions of pith, 

 giving them a jointed appearance, 

 whence the name. 



Leaves formed on the model of 



the rush have several advantages in 



northern regions. They are flexible, 



and not liable to be broken in storms ; 



Fig. 341.— Flower of their thick epidermis protects them 



junous articulatus. from cold ; they resist evaporation ; 



" '"^®*' ■ and they catch the low light which 



would not, as in temperate regions, fall on the upper 



side of the leaf. They would also be well suited to 



benefit by the low light glinting from the surface of 



the shallow water in which they so often grow. 



The fruit is an upright capsule from which the seeds 

 are jerked by the wind. It has three chambers, opening 

 by three valves which alternate with the walls. The 

 exterior walls of the pericarp are strongly lignified, and 

 their contraction causes the dehiscence. 



J. balticus. — This species flowers in pulses. 



J. bufonius. — Annual. In some districts — as, for in- 



' " Monographia Junoacearum, " Engler's Bot. Jahrb. xii. 



