432 
ISLAND LIFE. 
[part ji. 
meantime have acted as a fresh centre of dispersal ; and thus 
a plant might pass on step by step, by means of stations 
temporarily occupied, till it reached a district where, the 
“ Close by Ditton Station three species appeared which may be called 
interlopers. The biennial Barbarea pi'ecox , 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 
Petroselinum segetum was at first one very luxuriant plant on the slope of 
the embankment. It increased by seed into a dozen or a score, and is now 
nearly if not quite 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 Arabis hirsuta, likely to become a permanent inhabitant. The 
species is found on the chalk and greensand 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 
Arabis 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. 
Now there are several scores of specimens in the brickwork of the arch. 
It is presumable that the first seed may have been brought from Guildford. 
But how could it get on to the perpendicular face of the brickwork? 
“ The Bee Orchis ( Ophrys 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 greatly 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 within the limits of the adjoining 
parish of Cobham. I had crossed this same field in a former year without 
observing the 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 the temporary vegetation of the banks and cuttings on the 
