xviii THE CRATERS OF THE RIFT VALLEY 241 



perhaps fifteen or twenty years. Once a lobelia lias 

 readied the stage of producing a flower-spike and burst- 

 ing into blossom, it has reached the end of its life. It may 

 take twelve months for the spike to finish blossoming ; 

 then the whole plant withers and dries up, and probably 

 stands for several years before it falls and is swallowed 

 up by the moss. In L. Stuhlmanni the leaves as they 

 die fall off, leaving the stem bare except for green leaves. 



The (lower-column of a Tree-lobelia, 



L. T<ltkn, Kenia ; real size. 



The blossoms are shown open anil closed. The 



sepals arc bright green ; the petals, violet. 



In L. Deckenii none of the leaves fall off and the stem 

 is entirely concealed by them, from the ground up to 

 the spike, which has a much greater circumference than 

 in other lobelia. This species without its flower-stalk 

 often appears as a rosette of leaves squat on the 

 ground. 



In L. Woll'ixtoni some leaves fall off and others 

 remain hanging, so it usually has a portion of the stem 

 exposed. These differences in the relation of the dead 



R 



