I 



BIOLOGICAL TRAINING AND STUDIES. 857 



when a plot of ground whicli has for many years, or even genera- 

 tions, been devoted to carrying some particular vegetable growth, 

 whether grass or trees, has that particular growth removed from it. 

 When such a clearing is effected, we often see a rich or even a rank 

 vegetation of a kind previously not growing on the spot spring up 

 upon it. The like phenomenon is often to be noted on other sur- 

 faces newly exposed,, as in railway-cuttings and other escarpments, 

 and along the beds of canals or streams, which are laid bare by the 

 turning of the water out of its channel. Fumitory, rocket, knot- 

 grass or cowgrass (Tolygonum aviculare)^ and other such weeds, must 

 often have been noted by every one of us here in England as coming 

 into and occupying such recently disturbed territories in force ; 

 whilst in America the destruction of a forest of one kind of wood, 

 such as the oak or the chestnut, has often been observed to be 

 followed by an upgrowth of young forest trees of quite another 

 kind, such as the white pine — albeit no such tree had been seen for 

 generations growing near enough to the spot to make the transport 

 of its seeds to the spot seem a likely thing. In one case referred to 

 by Mr. Marsh, 'Man and Nature/ p. 289, the hickory, Cari/a 

 jjorcina, a kind of walnut, was remarked as succeeding a displaced 

 and destroyed plantation of the white pine. Now the advocates 

 of spontaneous generation must not suspect me of hinting that 

 there is any question, except in the minds of the grossly ignorant, 

 of the operation of any such agency as spontaneous generation here ; 

 no one would suggest that the seeds of the Polygonum avicularCy to 

 say nothing of those of the hickory, w^ere produced spontaneously; 

 but what I do say is, that the question of how these seeds came 

 there is just the very analogue of the one which they and their 

 opponents have to deal with. And it is not definitely settled at 

 this very moment. Let us glance at the instructive historical 

 parallel it offers. For the very gross and palpable facts of which 

 I have just spoken there are two explanations offered in works of 

 considerable authority. The one which has perhaps the greatest 

 currency and commands the largest amount of acceptance is that 

 which, in the words of De Candolle, regards la couche de ierre 

 vegetale d'un pays comme un magasin de graines, and supposes that m 

 hot summers and autumns, such as the present, the fissures in the 

 ground, which have proved so fatal this year to the young par- 

 tridges, swallow up a multitude of seeds, which are restored again 



