66o CONCLUSION 



evolution of the sporophyte was essentially different from that so constantly 

 seen in their individual development Here it is held that unless good 

 reason be found to the contrary, the development of the individual will 

 probably reflect in some degree the evolution of the race ; but it is 

 recognised that the principle is not directly applicable in all cases (Chapter 

 XIV.). 1 Accordingly the ontogenetic facts would support a view involving 

 the appearance of new structures in the course of descent. 



We have seen that the first steps in the organisation of a sporophyte 

 are suggested by the post-sexual divisions in certain Algae which there is 

 good reason to believe were associated with a reduction of chromosomes. 

 Passing from these initial stages of the sporophyte, of which the post- 

 sexual stage in certain Algae cannot be held as more than suggestive of 

 what actually occurred, to those where it appears as a more or less 

 extensive tract of tissue, it has been shown that the sporogonia of Bryo- 

 phytes provide numerous examples of sterilisation, and that the result has 

 been to defer the event of reduction, and in various ways to increase the 

 means of nutrition and dispersal of the spores (see pp. 258-286). The 

 facts of sterilisation and their biological results have been accepted by 

 other writers, and though they do not actually demonstrate that the 

 sporogonium of the Bryophyte did originate by intercalation of a new 

 phase in the life-cycle, nevertheless the observed facts harmonise with that 

 view : it is difficult, without having recourse, as some have done, to purely 

 hypothetical preliminary phases in the descent of this phylum, to read the 

 facts in any other way. 



One important point on which the Bryophyta differ markedly in their 

 individual development from all Vascular Plants, is that in them, as a rule, 

 the whole sporophyte originates by a primary embryogeny : it is initiated 

 directly from the zygote with the minimum of apical or intercalary growth, 

 and with entire absence of appendages. 2 There is no continued embryogeny, 

 with secondary initiation of fresh parts, as in Vascular Plants. This simple 



1 There are two leading features of development to which a theory of recapitulation 

 will not apply, and both are open to a biological explanation. The one is where those 

 gouty developments occur in the embryogeny, especially in the Lycopods (p. 351), the 

 other is the apparent priority of the vegetative system over the spore-production in the 

 individual life. In both cases the recapitulation of the sequence of developmental events 

 may be held to have been overruled by physiological requirement : the latter is fully 

 explained on the basis first of sterilisation of individual cells, and secondly of abortion 

 of the spore-producing parts : the consequence is that the vegetative system appears before 

 the spore-production begins : though the latter was the prior function of the sporophyte, 

 the overruling requirement was for early nutrition. The former has its origin in the 

 demands of early nursing of the embryo, and it has been shown that it has arisen 

 along two distinct lines within the genus Lycopodiiim. Such responses to biological 

 requirement are readily intelligible ; but they must not be held to invalidate the whole 

 doctrine of recapitulation, they show rather that it applies within limits only, and that 

 the evolutionary story which the individual may tell is liable to secondary disturbance. 



2 An exception is seen in Eriopiis. in which rhizoids appear at the base of the seta : 

 this appears to be a good example of the origination of new organs not fashioned out 

 of pre-existing organs (Goebel, flora, 1906, pp. 66, 68). 



