822 ON A NEW HYBRID POTAMOGETON OF THE FLUITANS GROUP. 



able to flower in the shallow ditch in which it grows. This ditch 

 has been carefully examined for water-plants by rne for some years 

 past, but no fluitans-formia were detected until the present season, 

 when I was surprised at finding numerous young plants, apparently 

 seedlings in their second year. As I at once saw by the thickly 

 coriaceous lower leaves that these young plants belonged to P. 

 crassifolius, I carefully examined the vegetation of the whole ditch, 

 which then contained water only two or three inches deep along its 

 whole course. At the upper end a single patch of P. natans grew 

 with here and there a plant of P. plantagineus, but neither of these 

 species was in flower, nor pushing up flower-spikes. About fifty 

 yards lower down the ditch P. Zizii became very abundant and 

 flowered freely, and amongst this species I found a single plant of 

 P. natans, which had spread out into a small patch, showing it had 

 occupied that station for some three or four years : immediately 

 below this, and for the distance of 60 or 70 yards, single young 

 plants of P. I crassifolius grew ; they were not scattered irregularly 

 over the bottom of the ditch, but grew on one side of it, just where 

 the flow of the water would carry the seeds when the drainage-mill 

 was at work. Now this ditch for some years has been completely 

 isolated from the main drain, into which it flows, except by a 

 narrow tunnel at the end of the ditch, through which no fragments 

 of plants or seeds could easily pass. No plants of crassifolius were 

 found at this lower end of the ditch, so it was evident that they 

 had not been introduced from the main drain. At this lower end 

 a few dwarf plants of P. lucens were growing, but the water was too 

 shallow, and had been for some years, to allow them to flower ; 

 besides, the plants of crassifolius did not grow near the lucens plants, 

 and there is no upward flowing of the water to have carried their 

 seeds to where the plants of crassifolius grew, even if they had been 

 able to flower. 



I have been thus minute in describing this locality, because it 

 affords one of the strongest proofs of natural hybridity in Potamo- 

 getons that it is possible to meet with. So thoroughly had this 

 particular ditch been examined by me for some years past that I 

 can safely affirm that these seedlings did not exist before the 

 summer of last year, when they would naturally be too small to 

 attract attention. 



Hitherto I had found it difficult to understand how a whole spike 

 of flowers could become fertilised by the pollen of another species of 

 Potamogeton, as the flowers in this genus do not seem to be usually 

 visited by insects ; and in fact, in the two species in question, the 

 spikes are frequently much interrupted by the abortion of many 

 ovules. The careful examination of the plants in this same ditch, 

 however, enabled me to arrive at a solution of the difficulty. A 

 single spike only of P. natans was produced on one of the plants 

 near the centre of the ditch, and of this the pistils were exserted and 

 receptive before any pollen was ripe. As no other spike of natans 

 occurred in the ditch, this solitary one must, if impregnated at all, 

 depend upon fertilisation by such pollen of P. Zizii as would be 

 carried to it by the wind, or by closely contiguous spikes of that 



