VII.—Studies in the morphology of spore-producing members.—No. V. General comparisons and conculsion

Abstract

In the series of Memoirs of which this is the fifth, and concluding part, the spore-producing members of all the important types of living Pteridophyta have been examined. But it will be well, before entering upon a full discussion of the results, to re-state the general problem of origin of the sporophyte generation, of which those members are so constant a feature. For since 1893, when the first Memoir of this series was written, many fresh facts bearing on the larger question have been disclosed, while a new face has been put upon the whole doctrine of alternation by the recognition of those differences of nuclear state, which have now been found in so many cases to accompany the alternating phases of the life history. Moreover, I am aware of having stated the problem in the first instance so that some of my expressions have been misunderstood, while others require amendment for other reasons. I therefore take the opportunity of first re-stating the general views upon which such data as have been acquired will have their bearing. There are two broad facts which form the basis of the whole discussion: first, that spore-production is the end to which the life of all typical sporophytes tends; and, second, that the sporophyte in all typical cases arises from the unicellular zygote. It is the generation thus initiated by the zygote, and tending uniformly to the production of spores, which is the subject of our present study, but especially the parts of it which produce the spores.