THE VITALITY AND DISTRIBUTION OF SEEDS 
303 
In conclusion, I may refer to some notable examples illustrating 
the problem under discussion. Of these, the London Rocket (Sisgni- 
brium Irio ) mentioned above is perhaps the most interesting. Its 
native habitat is possibly Afghanistan and Northern India, where it 
is abundant, but it has spread into Europe, where it is a weed of 
waste places and roadsides. Ray and Merrett expressly state that it 
occurred in the suburbs of London in the years preceding 1667, 
though then a recent introduction, and Parkinson in 1640 did not 
know of it as an English plant (Dunn, Alien Flora of Britain , 
1905, p. 29). It is an established fact that this plant frequently 
appears after tires, and also after the levelling of building-sites, and 
it seems likely that the seeds are derived from plants lurking in the 
immediate neighbourhood, which very rapidly spread over cleared 
spaces favourable to their growth. But how are we to account for 
the sporadic appearance of the plant upon building-sites through¬ 
out so many centuries P In my paper on the “ Flora of London 
Building Sites ” (Journ. Bot. 1912, 117) it is reported to have 
occurred in fair abundance in Bloomsbury. The houses cleared from 
this area had basements or cellars, but it is not likely that the soil 
under these contained the seeds; the probability is that the plant 
lurked in the back gardens or yards in the vicinity. It is not a plant 
which would catch the eye of any but a skilled botanist; and as 
botanists have little opportunity of investigating the flora of London 
back yards, it may still exist unobserved in the older parts of the 
City. 
Another well-known habitat of this plant is at Oxford. Baxter 
(Z. c. 116) tells us that, when alterations were being made in the 
Oxford Botanical Garden in 1831, rubbish was removed to a space 
outside the walls of the Garden, and was frequently burning for two 
or three days at a time, a considerable quantity of ashes being 
produced. These ashes were spread over the surface and dug in, and 
very shortly an abundant and very luxuriant crop of the Sisym¬ 
brium appeared, though never before seen in that part of the garden. 
From his account one infers that plants did occur in other parts 
of the Garden, and these no doubt provided the seeds for starting the 
new colony. 
During last winter a well 70 feet deep was dug at Saffron 
Walden, and the earth which was excavated became covered by a fine 
crop of Poppies; how did the seed get there P There are said to 
have been no Poppies previously in the immediate neighbourhood, 
and the crop followed so quickly after the excavation that one can 
scarcely escape the conviction that, in this case, the seeds must have 
been actually contained in the soil itself. This Poppy may, or may 
not, be one of the plants whose seeds retain their vitality for a very 
long period; but, in any case, poppies so frequently form part of 
rubbish-heap floras and hang about hedges or in odd corners that a 
few unobserved plants might within recent years have scattered a 
good supply of seeds on the site. Some years ago attention was called 
to the constant appearance of Poppies round about Cromer in Norfolk, 
