SOME PLANT BIOGRAPHIES. 199 



just what the frogs and newts and other animal in- 

 habitants of the pond do at the san:ie time to pre- 

 vent getting frozen. Next year the severed tops 

 send out roots in the soft mud of the bottom, and 

 grow up afresh into new green pondweeds. 



It is therefore impossible to make any broad 

 line of distinction in this way between what may 

 be considered as modes of individual persistence 

 in the self-same plants, and what may be regarded 

 as modes of reproduction by subdivision. Some 

 plants, like couch-grass and elm, are almost always 

 surrounded by young shoots which may ultimate- 

 ly become to all intents and purposes independent 

 individuals; while others, like corn -poppy or 

 Scotch fir, never produce any offsets or suckers. 

 In the meadow orchids each plant produces 

 every summer a second tuber by the side of the 

 old one ; and from the top of this tuber the next 

 year's stem arises in due time with its spike of 

 flowers. Here we may fairly regard the tuber as 

 a simple means of persistence in the plant itself; 

 there is nothing we could possibly call reproduc- 

 tion. But in many lilies the older bulbs produce 

 numerous small branch bulbs at their sides; and 

 these younger bulbs may become practically in- 

 dependent, each of them sending up in the course 

 of time its own stem and its own spike of flowers. 



Even when the main trunk of a tree is dead, 

 through sheer old age, it often happens, as in the 

 elm and birch, that the roots send up fresh young 

 shoots, which may grow again, and prolong the 

 life of the plant indefinitely. In stone-crops and 

 other succulent herbs, which grow in very dry and 

 desert situations, the merest fragment of a stem, 

 dropped on moist soil, will send out roots and 

 grow afresh into a new individual. Cactuses and 



