30 ANNUAL OF SCIENTIFIC DISCOVERY. 



have done. And on the other hand, it is found, that under existing circum- 

 stances, those Composites, which are disseminated throughout the area of* the 

 Great Pacific, belong in many cases to species destitute of these auxiliaries to 

 transmission. But here Geology comes to our aid ; for by pointing out the 

 probability of the submergence of continents on the one hand, and the eleva- 

 tion of tracts of land on the other, it enables us to explain the occurrence of 

 the same plants in some islands or continents now wholly ^unconnected, and 

 the existence of a distinct Flora in others too isolated to obtain it under 

 present circumstances from without. In the one case we may suppose the 

 plants to have been distributed over the whole area before its several parts 

 became disunited by the catastrophes which supervened ; in the other, we 

 may regard the peculiar Flora now existing as merely the wreck, as it were, 

 of one which once overspread a large tract of land, of which all but the little 

 patch upon which it is now found had since been submerged. However, 

 upon tin's subject our opinions may in some measure be swayed by the nature 

 of the conclusions we arrive at with respect to the length of time during 

 which seeds are capable of maintaining their vitality ; for if after remaining 

 for an indefinite period in the earth they were capable of germinating, it 

 would doubtless be easier to understand the revival, under favorable circum- 

 stances, of plants which had existed before the severance of a tract of land 

 from the continent in which they are indigenous. An inquiry has accor- 

 dingly been carried on for the last fifteen years under the auspices of 

 this Association, the results of which, it is but fair to say, by no means 

 corroborate the reports that had been from time to time given us with respect 

 to the extreme longevity of certain seeds, exemplified, as it was said, in the 

 case of the mummy-wheat and other somewhat dubious instances ; inasmuch 

 as they tend to show, that none of the seeds which were tested, although 

 they had been placed under the most favorable artificial conditions that 

 could be devised, vegetated after a period of forty-nine years ; that only twenty 

 out of two hundred and eighty-eight species did so after twenty years ; whilst 

 by far the larger number had lost their germinating power in the course of ten. 

 These results, indeed, being merely negative, ought not to outweigh such 

 positive statements on the contrary side as come before us recommended by 

 respectable authority, such, for instance, as that respecting a Nelumbium seed, 

 which germinated after having been preserved in Sir Hans Sloane's Herbarium 

 for one hundred and fifty years ; still, however, they throw suspicion as to the 

 existence in seeds of that capacity of preserving their vitality almost indefi- 

 nitely, which alone would warrant us in calling to our aid this principle in 

 explaining the wide geographical range which certain species of plants affect. 

 Let us then be content to appeal to those ingenious views which were first 

 pat forth by the late Professor Forbes. By the aid of the principles laid down, 

 he was enabled to trace the Flora of Great Britain principally to four distinct 

 sources, owing to the geological connexion of these islands at one period or 

 other with Scandinavia, with Germany, with France, and with Spain! And 

 it was by a similar assumption that Dr. Joseph Hooker explained the dis- 

 tribution of the same species throughout the islands of the Great Pacific, and 

 the contiguous continents, tracts which, as Darwin had shown, were formerly 



