NUPHAR INTERMEDIA IN BRITAIN 



23 



capacity of Nuphar to reproduce vegetatively is well known. The bottom of Chartners 

 Lough in the area of the Nuphar is entirely covered with entangled rhizomes, and although 

 verification would appear now to be impossible, it does not seem inconceivable that all 

 are ramifications of a single huge plant. If so, the age of this plant must be enormous, 

 far exceeding the century or so for which individual Nuphar plants have been observed 

 to persist in cultivation. 



No seedlings were noted in the Chartners Lough colony, and it is quite obvious 

 that, under the existing conditions, seedlings would find considerable difficulty in estab- 

 lishing themselves against the competition of the mature plants, particularly for light. 

 Nevertheless the successful germination of seeds from the fruits of the season of 1952 

 shows that propagation by this means is at least feasible. The low pollen and ovule 

 fertility points to the probability that severe meiotic irregularities are present, arising 

 possibly from structural differences between the parental chromosomes. If so, it is 

 possible that genetical recombination is severely limited, and that only those spores 

 survive and function which approach a particularly favourable genetical balance. 



It may be that the uniformity of such colonies as the Chartners one is maintained 

 by a combination of several factors - by the extensive occurrence of vegetative propagation 

 of successful plants, by the fact that only a limited amount of genetical recombination is 

 possible, and by the stringent elimination, through competition, of ill-adapted seedlings. 



Anomalous populations 



A comment on the Avinlochan colony seems appropriate at this point. This colony 

 has usually been accepted by systematists as falling within the range of N. pumila, and 

 was so in the course of the present study until it was realised that it combined a relatively 

 low pollen fertility with certain anomalous features not encountered in other populations 

 of N. pumila. Accordingly, the biometrical data relating to this colony have been kept 

 separate in the tables and not incorporated in the N. pumila aggregate. Considering all 

 of these data, it will be seen that the Avinlochan colony does, in fact, in its morphological 

 features depart somewhat from the other colonies of N. pumila in the direction of N. 

 lutea. This and the depressed fertility would seem to indicate that it has in the past suffered 

 genetical contamination from N. lutea. The ovary fasciation illustrated in Fig. 6 is 

 present to a greater or lesser degree in the bulk of individuals of the colony, and must be 

 looked upon as sub-pathological. A similar, but even more extreme, example of the 

 incidence of ovary fasciation of this type was encountered by Caspary (1870) in a colony, 

 referred to N. pumila, in Titisee. Caspary's data suggest that there is a considerable 

 amount of variation within and amongst the Nuphar populations of the lakes of the Vosges 

 and the Black Forest, and here again the possibility of different degrees of introgression 

 of N. pumila and N. lutea is present. The great variation in pollen fertility observed 

 by Caspary in these colonies points in the same direction. 



The distributional problem of N. intermedia 



The final problem concerns the existence of N. intermedia in localities like Chartners 

 in isolation from one or both parents - a circumstance, in the case of the Chartners colony, 

 once considered to rule out the possibility of its being of hybrid origin (Baker and Tate, 

 1868). Once again there is more than one possible explanation. The simplest would be 

 that colonisation has arisen relatively recently from a chance hybrid seed carried by 

 some agency - presumably water-fowl - from a locality where the two parents exist today 

 in close proximity. While this explanation cannot altogether be rejected, it would seem 

 improbable. With the Chartners colony the minimum distance of transport would have 

 to be of the order of 80-90 miles and it would seem to be pressing the idea of chance 



