Fig. 3. 



Potaniogefon crispus X P. praelonr/iis (P. undnlatus). 



A. transversal section of the stem (^^/i); Icj. lacunae; hh. vascular bundles 



in the hark; c. axial cylinder. B—C. transverse section of the axial 



cylinder (^Vi): the white parts: vascular bundles; the hatched parts: 



pith; Ig. lacuna? in the vascular bundles. 



As to the nervure of the leaves , P. undulatus (25 B) 

 [Fig. 4, B] is just between P. crispus (25 A) [Fig. 4, A] and 

 P. praelongus (25 C) [Fig. 4, C]. As to the margin of the 

 leaves , P. perfoliatus has at least most frequently leaves 

 with dentate margins and the leaves of P. crispus are always 

 serrulate (25 A) [Fig. 4 A']. In a hybrid between these two 



Fi^.4. 



Tips of the leaves of: A. Potamogeton crispus. 



B. P. crispus X P. praelongus. C. P. praelongus. (^/i.) 



