I may, however, indicate the line of defence I should take were I to go again into the matter. The objections are based on the structure of existing Liverworts and Phænogams. But I have already referred to the probability--or, indeed, the certainty--that in conformity with the general principle set forth in the note to Chapter I, we must conclude that the early types of Liverworts out of which the Phænogams are supposed to have evolved, as well as the early types of Phænogams in which the stages of evolution were presented, no longer exist. We must infer that forms simpler than any now known, and more intermediate in their traits, were the forms concerned; and if so, it may be held that the incongruities with the hypothesis which are presented by existing forms, do not negative it. The scepticism my critic himself expresses respecting the current interpretation is a partial justification of this view. Moreover, his admission that the theory set forth “fits in well with the phenomena exhibited by phanerogamic shoots,” must, I think, be regarded as weighty evidence. On the Evolution hypothesis we are obliged to suppose that the Monocotyledons and Dicotyledons respectively arose by integration of fronds; and if to the question after what manner the integration took place, there is an hypothesis which renders it comprehensible, and agrees both with the structures of the two kinds of shoots and the structures of the two kinds of seeds, as well as with various of the other phenomena the two types present, it has strong claims for acceptance. Reconsideration suggests the following remarks. 1. Alternation of generations is a means of furthering multiplication. To be effective each member of either generation must be a self-supporting centre of growth or diffusion or both. Hence if, as in the Liverworts, one of the so-called alternating generations is not independent, but a permanent growth on the other--a parasite--it is a misuse of words to call the arrangement Alternation of generations. (Since this was written I have found that Sir Edward Fry takes the same view. He approvingly quotes Professor Bower, who says that “the alternation of generations is not an accurate statement of facts or a useful analogy.”) 2. The alternating of sexual and non-sexual processes is not fundamentally distinctive; for, as shown by sundry Archegoniates, it is an inconstant trait, and as shown by Klebs’ experiments on _Vaucheria_, the conditions may be varied so as to determine its occurrence or non-occurrence. Nay, the same individual may reproduce in either way. 3. Still more significant is the fact that in some of the marine Thallophytes, there is a process like that which in a moss or a fern is considered an alternation of generations, whereas in others, as the Brown Wrack (_Fucus_), each generation is sexual. Thus the presence or absence of this mode of genesis cannot be a cardinal distinction.