PDF - Wallace Online

CREATION BY LAW 147inches, and was chiefly fertilisedby a species of moth whichappeared at the time of the plant's flowering, and whose probosciswas of the same length. Among the millions of flowersof the Angrsecum produced every year, some would always beshorter than the average, some longer. The former, owingto the structure of the flower, would not get fertilised, becausethe moths could get all the nectar without forcing theirtrunks down to the very base. The latter would be wellfertilised, and the longest would on the average be the bestfertilised of all.By this process alone the average lengthof the nectary would annually increase, because, the shortnectariedflowers being sterile and the long ones havingabundant offspring, exactly the same effect would be producedas if a gardener destroyed the short ones and sowed the seedof the long ones only ;and this we know by experiencewould produce a regular increase of length, since it is thisvery process which has increased the size and changed theform of our cultivated fruits and flowers.But this would lead in time to such an increased lengthof the nectary that many of the moths could only just reachthe surface of the nectar, and only the few with exceptionallylong trunks be able to suck up a considerable portion.This would cause many moths to neglect these flowersbecause they could not get a satisfying supply of nectar, andif these were the only moths in the country the flowers wouldundoubtedly suffer, and the further growth of the nectary bechecked by exactly the same process which had led to itsincrease. But there are an immense variety of moths, ofvarious lengths of proboscis, and as the nectary became longer,other and larger species would become the fertilisers, andwould carry on the process till the largest moths became thesole agents. Now, if not before, the moth would also beaffected, for those with the longest probosces would get mostfood, would be the strongest and most vigorous, would visitand fertilise the greatest number of flowers, and would leavethe largest number of descendants. The flowers most completelyfertilised by these moths being those which had thelongest nectaries, there would in each generation be on theaverage an increase in the length of the nectaries, and alsoan average increase in the lengthof the probosces of the