v] WINTER-BUDS OF THE PONDWEEDS 69 



42 A and B were drawn from a bud which had passed the 

 winter at the bottom of a rain-water tub in the present writer's 

 garden. The turions of this species seem to be primarily repro- 

 ductive bodies, and to be only secondarily concerned with 

 tiding over the winter, for large numbers germinate without a 

 resting period. Not only the rhizomes, but certain of the leafy 

 shoots, are capable of lasting over the cold season, if they are 

 not actually frozen. The special winter branches differ some- 

 what from the summer shoots 

 in having leaves without a 

 crisped margin, and they have 

 hence been sometimes mis- 

 taken for a distinct species. 



A second group of Pond- 

 weeds is characterised by 

 winter-buds whose enclosing 

 scales consist merely of axil- 

 lary stipules, the correspond- 

 ing blades having wholly 

 disappeared. Fig. 44 repre- 

 sents a transverse section 

 of a turion of Potamogeton 

 rufescens^ which conforms to 

 this type. In this species the 

 winter-buds are formed 

 chiefly on the underground 

 rhizome, while in P.fluitans^ 

 Roth a species closely re- 

 lated to P. nutans they 

 occur in this situation only. 



Potamogeton perjoliatus^ L. 

 forms winter-buds which are 

 not deciduous but unfold in 

 situ (Fig. 36, p. 59). 



In flower structure^, as well as in anatomy, a reduction series 



iSchenck, H. (1885). 



Fig. 44. Potamogeton rufescens, Schrad. 

 T.S. through a turion. A and B, outer 

 scale leaves equivalent to stipules; I-IV, 

 foliage leaves, whose stipules are marked 

 1-4 and put in in solid black. Squamulae 

 intravagino.les are omitted. (Enlarged.) 

 [After Gliick, H. (1906), Wasser- und 

 Sunipfgewachse, Bd. 11, p. 160, Fig. 23.] 



