32 PLANT-LIFE ON LAND [CH. 



this is short as in the Shield-Fern the leaves appear 

 as a compact tuft, where it *is long they are isolated, 

 Avhile the stem may be either exposed to the air or 

 it may run underground as in Pteridiam. 



An examination of a number of rhizomes will show 

 that the stem is capable of indefinite growth in length, 

 but occasionally it forks at the tip into two exactly 

 equal branches. It is plain that by this means the 

 shoot-system may be enlarged, but a more effective 

 way is that which is more common in the Bracken, 

 viz. by the formation of a new bud near the base of 

 each leaf-stalk. Since each such bud is potentially 

 a new shoot endowed with apical growth like the 

 original, it is apparent that there are ample powers of 

 extension of the shoot-system. On the other hand, if 

 a stem be followed backwards from its apex, sooner 

 or later a region will be reached where the tissues 

 will be no longer fresh and living. The fact is that 

 decay is constantly progressing from the base upwards, 

 and whenever it extends beyond a bifurcation or the 

 insertion of one of the leaf-buds there will be a 

 complete severance of the two living apical regions, 

 and two individuals, physiologically independent, will 

 result. In this way the Bracken may spread over 

 large areas of ground, its development being simply 

 vegetative. In fact those large sheets of its growth 

 which occupy wide stretches of hillside and woodland 

 owe their origin to continued growth of individuals 



