SHOOTS 



59 



independent plants by the dying of tlie runners (see Figs. 

 47, 48). 



45. The floating type. — In this case the stems are sus- 

 tained by water. Numerous illustrations can be found in 

 small inland lakes and slow-moving streams (see Fig. 40). 

 Beneath the water these stems often seem quite erect, but 



Fig. 49. A submerged plant {Ceratophyllum) with floating stems, showing the stem 

 joints bearing finely divided leaves. 



when taken out they collapse, lacking the buoyant power 

 of the water. Growing free and more or less upright in 

 the water, they seem to have all the freedom of erect stems 

 in displaying foliage leaves, and at the same time they 

 are not called upon to build rigid structures. Economy 

 of building material and entire freedom to display foliage 

 would seem to be a happy combination for plants. It must 

 be noticed, however, that another very important condition 

 is introduced. To reach the leaf surfaces the light must 

 pass through the water, and this diminishes its intensity so 



