356 



THE UNIVERSE. 



the lungs of plants. It is seldom that they are unprovided 

 with them, yet such is the case with some Euphorbia), the 

 stem of which, inordinately swollen, entirely replaces them, 

 and only bears very insignificant rudiments of such struc- 

 tures. 



165. Aerial or Pulmonary, and Aquatic or Branchial, Leaves of the Aquatic Ranunculus. 



The leaf is composed of two parts : the petiole, or sup- 

 port, and the blade, which is spread out in the form of a 

 membrane. It is only exceptionally that this is perforated 

 so as to look like an elegant net-work, as in the Hydrogeton 

 fenestration, the name of which comes from this singular 

 peculiarity ; it is also seen in the submerged leaves of some 

 aquatic plants, which in such an arrangement seem to re- 

 mind us of the branchiae, the respiratory organs of fish. 



In some plants they are transformed into long capillary 

 filaments, which are seen gently undulating in the current 

 of our rivers, like the tresses of a naiad floating beneath 



