338 



EXPERIMENTS WITH PLANTS 



shaped leaf, a transition form between the two. Fig. 

 194 shows at (b) a section of a submerged portion of 

 a ribbon- like leaf, while at (a) is a section of a por- 



194. Cross-section of the ribbon-shaped leaves of Arrowhead, (a) from a part of 

 a leaf above the water, (6) from a part of a leaf below the surface, showing 

 thinness , lack of cuticle and larger air-spaces. 



tion of a ribbon-like leaf which projected into the air. 

 Fig. 195 (a) shows a submerged leaf (water -leaf) of 

 the Water Buttercup, while beside it (b) is another 

 leaf which grew above the water ( air- leaf ) . The Water 

 Buttercup presents a transition from a land- plant to a 

 water-plant. If the water sinks, so that the sub- 

 merged leaves are exposed to the air, they dry up and 

 perish, while the air -leaves live on and the plant 

 continues to flourish. 



We have good reason to believe that the water- 

 plants (with the exception of Certain groups of flow- 



