Fig. 33: Potamogeton pectinatus: a, moniliform spike with mature achenes, X 1%; 

 b, habit, showing slender branching stems and linear-filiform submersed leaves, arising 

 from rhizome, X %; c, upper flowers of spike, X 4; d and e, variation in achenes 

 (usually obliquely ovoid, with a short wartlike beak), d, X 5%, e, X 5; f, achene 

 (longitudinal section), X 5; g, stipules sheathing stem or loosely investing it and some- 

 what inflated, the linear leaf appearing to originate at the top of the sheath, X 3; h, 

 rhizome with winter corm, X lYr,. (From Mason, Fig. 14). 



