796 



THE DISTRIBUTION OF SPECIES BY OFFSHOOTS. 



(Helianthus tuberosus) the tuber- forming shoots are short; the colony is therefore 

 crowded, and only spreads slowly over a larger area. The Alpine Enchanter's 

 Nightshade (Circcea alpina; see fig. 444 s ) forms elongated tubers at the end oi 

 shoots 6 cm. in length, about 5 of them round the mother-plant, whilst each of th< 

 new plants arising from these tubers repeats this formation in the same colony 

 Since 6 cm. is a considerable length compared with the size of the Enchanter's 

 Nightshade, the group is scattered and in a few years extends over a considerable 

 area. The tuber formation of Thladiantha dubia, a gourd-like plant growing in 



Fig. 444,-Plants with tubers and bulbs whose mode of growth leads to the formation of colonies arranged in lines and 

 clusters. 1 Muscari racemosum. 2 Thladiantha dubia. 3 Qirccea alpina. 



Eastern Asia, is especially luxuriant; its shoot-formation is shown in fig. 444 \ In 



this plant a whole -series of tubers which are chained together by thin threads 



8 cm. long is formed on each shoot. Usually they form series of 5-10, and such 



am is about 50 cm. long. As a new plant grows from each tuber and again 



duces chains of underground tubers, the Thladiantha in a few years may occupy 



an area of 10 sq. metres, and will form a cluster which is both crowded and rapidly 



mcreasmg in circumference. A further excellent example of the same thing is 



K*U* rn^ma which often spreads in the most diagrammatic manner in bare 



sandy places near the sea-shore. 



Many tuber-forming plants producing clustered colonies inhabit marshes, espe- 



such M are liable to great alteration in the level of the water and are 



m years of drought to the danger of temporarily drying up. Many Pond- 



