1036 KEPORT— 1898. 



estimate its probable importance as regards the Bryopbyta. It cannot fail to 

 strike the observer how uniform is the alternation in these plants ; there are, I 

 believe, no recorded cases of deviation from the normal alternation in Liverworts. 

 I know of only a single case of fipospory among Mosses taken in the open, and 

 then in atrophied capsules ; apospory, when induced, follows such extreme 

 treatment as chopping the sporogonium into pieces. And it is not as if the 

 Mosses and Liverworts bad escaped detailed observation ; hardly any group of 

 plants has been more carefully examined by competent observers. Deviations 

 from strict alternation then are rare, and appear under physiological stress. 

 This great group, which includes the simplest sporophytes among Archegoniate 

 plants, is also singularly constant in its alternation. I think this is to be 

 connected with the permanently dependent condition of the sporophyte ; its 

 equable physiological condition, nursed and protected by the Moss plant, finds its 

 morphological expression in its comparative uniformity. Conversely, the inde- 

 pendent position of the sporophyte in Ferns, and its exposure to varied conditions, 

 may have elicited more freely in them unusual developments. 



III. Abnormalities. 



And now I may pass to my third point, and discuss more generally the argu- 

 ment from abnormalities. I have no wish to prejudge the question by the use of 

 this term as applied to apogamy and apospory, or in any way to detract from their 

 morphological importance — I merely intend to express that they are departures 

 from that order of events which is the most frequent in Archegoniate plants at 

 large, and I particularly wish to point out that while such irregular developments 

 are now shown to be frequent in Ferns, they are exceedingly rare in Bryophytes, 

 and are not, I believe, hitherto recorded for Lycopodinese or Equisetinese. 



While direct vegetative transitions from one generation to the other may appear 

 &S, & prima facie support of an homologous origin of the two generations, I must 

 protest against their being used, as they have been, as evidence against an anti- 

 thetic view. It has been said that the facility with which these transitions 

 from one generation to another in Ferns take place ' shows that there is no 

 such hard and fast distinction between the generations as the antithetic theory 

 would appear to demand.' Why should it demand a hard and fast distinction ? 

 For my own part, I had already described apogamy and apospory as occurring in the 

 same individual before I wrote on alternation. The presumption seems to be 

 tbat a distinct course of evolution must have imposed ' bard and fast' limits upon 

 the potentialities of the parts evolved. But we ought to remember how the root, 

 whether in Phanerogams or Ferns, has doubtless had a long course of evolution 

 as a member distinct from the shoot ; and yet we see it bearing adventitious buds 

 upon it, as in the Rosacese, Poplar or Elm ; or even transformed at its apex into 

 a shoot, as in Platycerium or Anthurium. Such cases as these, though not exact 

 parallels, should suffice to show that hard and fast lines are not to be anticipated 

 as a consequence of a distinct course of evolution. 



There is another kindred, though almost converse, proposition which has been 

 advanced by Pringsheim. lie made his experiments on Moss fruits, ' in the hope 

 that he would succeed in producing protonema from the subdivided seta of the 

 Mosses, and thus prove the morphological agreement of seta and Moss-stem.' The 

 point here appears to be that parts which are capable of producing similar growths 

 are in ' morphological agreement.' I cannot assent to this proposition. In the 

 case of the roots above quoted, the production of buds upon them, or the conver- 

 sion of their apices into shoots, does not prove their ' morphological agreement ' 

 with shoots upon which sucb developments are common. 



By those who use such arguments it is to be borne in mind that the two 

 generations, however distinct in their evolution, are still merely stages in the life- 

 history of one and the same organism. The hereditary qualities of the race as a 

 whole must be transmitted through the successive generations. It may be a 

 question how far, and under what' conditions, its various potentialities come into 

 evidence, as, for instance, in the formation of an apogamous sporophyte, or of an 



