SHOOTS 



59 



indeiiendent plants by the dying (^f tlie runners (see Figs. 



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

 tained by water. Xunierous illustrations can be found in 

 small iidand lakes and slow-moving streams (see Fig. 4'.J). 

 Beneath the water these stems often seem quite erect, but 



~T) 



Fig. 49. A submerged plant {Ceratophyllnm) with floating stems, sliowiug the stem 

 joints bearing finely di\'ided leaves. 



when taken out tliey ('(dlapse, lacking the liuoyant power 

 of the water, tl rowing 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 c(.inditiMn 

 is introduced. To reach the leaf surfaces the light must 

 pass througli tlie water, and this diuiinishes its intensity so 



