ON A NEW HYBRID POTAMOGETON OP THE FLUITANS GROUP. 323 



species being brought into actual contact with it by the force of 

 winds or the movements of aquatic animals. 



As far as I have been able to observe, the anthers and stigmas of 

 Potamogetons sometimes ripen together, and sometimes one or the 

 other ripens first, or the stigmas in succession. Here, then, we 

 have a clue to the irregular fertilisation of the spikes in this 

 genus, and an explanation of how a spike of ripe pollen of one plant 

 accidentally dashed against the receptive spike of another plant 

 in which the pollen was immature might fertilise every ovule. By 

 actual experiment I have seen how easily this might be done ; and 

 whoever has watched the movements of a water-rat will readily 

 understand how contiguous spikes may be brought into contact 

 with sufficient force to dust every stigma with pollen. 



In this Westmoor variety of P. crassifolius the upper floating- 

 leaves are narrowly oblong-lanceolate, and make a decided approach 

 to those of narrow-leaved forms of P. natans, and, although they 

 have no discoloured joint, they often bend back like those of natans. 

 This variety grows freely under cultivation, but has shown no signs 

 of flowering as yet. 



One other form of P. crassifolius deserves mention, because it 

 shows some indications of partial fertility, as the drupelets swell to 

 some extent, and do not decay like those of P. decipicns and other 

 infertile hybrids. These immature drupelets were gathered too young 

 to afford any specific characters ; they may be roughly described as 

 oval-oblong with compressed sides, bluntly keeled on the back, with 

 a turgid beak broad in proportion to the rest of the fruit. All 

 these characters, however, may have little permanence, and be 

 merely the characters of immaturity. The upper floating-leaves of 

 this variety are orbicular-ovate, and somewhat ribbed on the under 

 surface, like those of natans. The young growth is that of typical 

 crassifolius. 



Besides in its parentage, P. crassifolius differs from P. fiuitans 

 Both in the following respects : — The mature lower leaves are 

 opaque and coriaceous like the upper ones ; in many instances they 

 are not at all membranous even in the earliest stages, but are 

 leathery in texture from the first ; they are usually all decayed by 

 the time the plant is in flower, and the whole plant decays by the 

 end of August, at which time P. fiuitans is in full growth. Although 

 the whole mass of foliage floats near the surface at the time of 

 flowering, even the uppermost floating-leaves are partly submerged, 

 like those of P. coriaceus, none growing so fully exposed to the air 

 as those of fiuitans and natans. The upper leaves are more dis- 

 tinctly auricled at the base, and are more abruptly narrowed into 

 the petiole, and the lamina is oval and bluntly mucronate, instead 

 of lanceolate or elliptical and acuminate. The petiole is flat above, 

 not conspicuously convex as in fiuitans. And lastly, the stipules 

 are flat on the back instead of being deeply grooved, and are "fibro- 

 scarious," and soon decaying like those of natans. 



I have seen no plant in any herbarium which I can refer to 

 /'. crassifolius, so at present I can only record it from the parishes 



v 9, 



