228 



Fig. 3. 



Potamogeton crispus X P. praelongus (P. undulatus). 

 A. transversal section of the stem ( 15 /i); lg. lacunae; bk. vascular bundles 

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

 cylinder ( 45 /i); the white parts: vascular bundles; the hatched parts: 

 pith; lg. lacunæ 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, 0]. 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 



Fig. 4. 



Tips of the leaves of: A. Potamogeton crispus. 

 B. P. crispus X P. praelongus. C. P. praelongus. ( 2 /i.) 



