514 ISLAND LIFE part ii 



will, in the meantime, have acted as a fresh centre of dis- 

 persal ; and thus a plant might pass on step by step, by means 

 of stations temporarily occupied, till it reached a district 



There were two or three plants of it at first, never more than half a dozen. 

 Once since I saw a plant of Isatis on the railway bank near Vauxhall. 



"Close by Ditton Station three species appeared which may be called 

 interlopers. The biennial Barharea prccoo:, one of these, is the least 

 remarkable, because it might have come as seed in the earth from some 

 garden, or possibly in the Thames gravel (used as ballast). At first it 

 increased to several plants, then became less numerous, and will soon, in 

 all probability, become extinct, crowded out by other plants. The biennial 

 Pctrosdinum segchwi was at first one very luxuriant plant on the slope of 

 the embankment. It increased b}'' seed into a dozen or a score, and is now 

 nearly if not (juite extinct. The third species is Linaria purpurea, not 

 strictly a British plant, but one established in some places on old walls. 

 A single root of it appeared on the chalk facing of the embankment by 

 Ditton Station. It has remained there several years and grown into a 

 vigorous specimen. Two or three smaller examples are now seen by it, 

 doubtless sprung from some of the hundreds or thousands of seeds shed 

 by the original one plant. The species is not included in Salmon and 

 Brewer's Flora of Surrey. 



"The main line of the railway has introduced into Ditton parish the 

 perennial Arahis hirsxita, likely to become a permanent inhabitant. The 

 species is found on the chalk and gi-eensand miles away from Thames 

 Ditton ; but neither in this parish nor in any adjacent parish, so far as 

 known to myself or to the authors of the flora of the county, does it 

 occur. Some 'years after the railway was made a single root of this 

 Arahis was observed in the brickwork of an arch by which the railway is 

 carried over a public road. A year or two afterwards there were three or 

 four plants. In some later year I laid some of the ripened seed-pods 

 between the bricks in places where the mortar had partly crumbled out. 

 Xow there are several scores of specimens in the brickwork of the arch. 

 It is presumable that the first seed may have been brouglit from Guildford. 

 But how could it get on to the perpendicular face of the brickwork 1 



" The Bee Orchis (Opkrys apifera), plentiful on some of the chalk lands 

 in Surrey, is not a species of Thames Ditton. or (as I presume) of any 

 adjacent parish. Thus, I was gi'eatly surprised some years back to see 

 about a hundred examples of it in flower in one clayey field either on the 

 outskirts of Thames Ditton or just Avithin the limits of the adjoining 

 parish of Cobham. I had crossed this same field in a former year \vithout 

 observing tlie Ophrys there. And on finding it in the one field I closely 

 searched the surrounding fields and copses, without finding it anywhere 

 else. Gradually the plants became fewer and fewer in that one field, 

 and some six or eight years after its first discovery there the species had 

 quite disappeared again. I guessed it had been introduced with chalk, 

 but could obtain no evidence to show this." 



4. Mr. A. Bennett, of Croydon, has kindly furnished me with some 

 information on tlie temporary vegetation of the banks and cuttings on the 

 railway from Yarmouth to Caistor in Norfolk, where it passes over exten- 

 sive sandy Denes with a sparse vegetation. The first year after the 

 railway was made the banks produced abundance of (Enothera odorata 



