328 ABNORMALITIES OF THE LIFE-CYCLE [CH. 



meiosis are knit together by the closest physiological ties. The latter is the 

 complement of the former. In like manner there is a relation between 

 apospory and apogamy. So far as our present knowledge goes apospory is 

 always found to imply the absence of meiosis from the life-cycle of the 

 organism. Consequently after apospory apogamy is inevitable. But it does 

 not follow that after apogamy there must be apospory. This is shown by 

 the case oiNephrodiMU Filix-vias, vd.x.polydactyla, Dadds. On the other hand 

 it would appear highly undesirable to see in such irregularities of the life- 

 cycle as those described direct evidence suitable for morphological or phyletic 

 argument. Their instability and sporadic occurrence precludes it. It has 

 been seen that apospory may be initiated from the sporangium, or from the 

 vegetative tissue of the leaf. That certain Ferns may sometimes follow the 

 normal cycle, and at others show apogamy {Marsilia Druminondii). Further 

 that apogamy may be carried out in different ways : for instance by migration 

 of nuclei {Ncp/irodinm Filix-nias, van polydactyla) ; or by direct vegetative 

 growth from a diploid source a diploid apogamous bud may arise {Athyriujii 

 Filix-foemina, var. clarissima, Bolton); or again from a haploid source a 

 haploid apogamous bud {Nephrodium mode, and hirtipes). But the most 

 important objection of all to their direct use in comparison with a view to 

 phylesis lies in the fact, that no definite phylum or line of Descent has been 

 permanently established showing any of these aberrant characters as a 

 constant feature. Such considerations will prevent these irregularities of the 

 life-cycle being used in serious morphological or phyletic argument. Their 

 value lies in the fact that they illustrate what is practicable in the chromo- 

 some-cycle, and so they tend to relax a too rigid conception of it. 



They also provide physiological suggestion. Observations on induced 

 apospory are cases in point. When first apospory was described it was 

 thought that it was specially related to the adult leaf, and particularly to 

 the fertile parts of it. Repeated attempts were accordingly made to induce 

 it in pieces of the sporophylls of many Ferns, but without any result {Amt. 

 of Bot. Vol. iv, p. 169). There appears to be a marked disability in the adult 

 leaf for bridging over the limit between the generations in any other way 

 than by spores= But it is different with the juvenile leaf Von Goebel {Experi- 

 inentelle Morphologie, 1908, p. 197, etc.) has shown how readily the primordial 

 leaves of various Ferns form aposporous prothallial growths (Fig. 304). This 

 clearly points to an essential difference between the juvenile and the adult 

 states. The latter seem to be more limited in their potentialities than the 

 former. 



It will naturally be asked, what bearings have these facts of apospory 

 and apogamy as seen in the Filicales upon any general theory of alternation? 

 The reply may be in the form of another question : are we justified in having 

 any "general theory of alternation" applicable to plants at large? It is a 



