90 



NA rURIi 



[NoVEMHliK 24, 1898 



llmiwii mil nficsh llml they may iciilly \w " ilcj;cncmle ilc- 

 sci'iul:iiils !>(■ lii|;lK'i rdiins." * 



III view ol' sUiliniciils MU-h as these it may lie well to examine 

 the liryopliyla <iiiile separately, without reference tn Vascular 

 riants at all, ami see what are their main bearini;s un theories 

 of alleinalion. Ami if tlie Hryophyles were the only Arche- 

 j;oniale Plants in the world, 1 think the case for llieir origin by 

 a progressive antiihetic alternation wouKI he an uncommonly 

 strong one ; the points which are especially noteworthy are : 



(1) The rea.liiiess with which they may lie ariaiij;eil in natural 

 sequences which illustrate increasing vei;elalive complexity of 

 the sporophyte as a eonseiiucnce of progressive sterilisation ; 



(2) The nuclear ilelails, which are as yet known, however, in 

 only lew cases : {31 The constancy of the two allernatiiiK 

 phases, the relations of which are very seldom disturbed by 

 iipospory, and never, to my knowledge, by apo|;amy. 



The lirst of these matters has been dealt with at length in my 

 "Studies." It is, of course, possible for any one to read such 

 sciiuences as are there mentioned in reverse order, and to uphold 

 a theory of simplilication ; but this must be shown to lie in 

 accordance with probability. Now it appears to me that the 

 general prolmbility in the case of the llryophytes is against sim- 

 plilicalion, for the linger the number of .spores which can be 

 maiureil the greater the prolmbility of survival ; even in cases 

 where, as in />'«> Ai«/hi.i and /'///jim. ;'«w, there is an exiguous, 

 and probably reiluced Moss-plant, the sporogonium is not of a 

 reduced lype, but, on ihe contrary, unusually large. It seems 

 10 mv mind uuich nunc probable that the Ihyophytesasa whole 

 illustrate a course of progressive complexity. .\ comparison of 

 anatomical iletails freiiuently suggests a progressive sterilisation, 

 a process which we see demonstrated both in I'leridophytes and 

 rhanerognins, where actual conversion of potentially s|H)r(i- 

 genous ti.ssue into temporary or permanent vegetative tissue 

 does occur. When it is added that the nuclear evidence, scanty 

 though it still is, .shows the sporophyte with a double number of 

 chromosomes, and the reduction taking place on the tetrad 

 division of the spores, the coimuuison w ith the segmented tygotes 

 of Algae and 1-ungi above mentioned seems inevitable. The 

 position of those who hold views of antiihetic alternation will, 

 therefore, be that the simple sporogonium was produced as a 

 poslsexual growth. The starting-point was probably some such 

 multicellular body as we see nowadays in certain .Mgae and 

 I'lingi resulting from division of the zygote, but not necessarily 

 homogenetic with any such body that we know now living. The 

 land habit imposed a restiiction on fertilisation, and an altern- 

 ative metluHl of incrca.se in numbers was an advantage. The 

 iiiulticelhilar body resulting from division of the zygote provided 

 the means for this : the cells develo|ieil separately as dry, dusty 

 spores. .\s the numlier of divisions lucieased, the powers of the 

 plant to nourish, protect and disseminate the spores became the 

 measure of the number produced. Hence lollowed the elabora- 

 tion of the nourishing and dis.seminating mechanism, which has 

 involved a diverting of some cells from their lirst olVice of spore- 

 prviduction, the start being, perhaps, made in a manner similar 

 to Ihe formation of the peridium in the I'redinea-. To my 

 mind — taking ihe Hryophyla alone— there is an inherent prob- 

 ability in all this, w hich tar counterbalances any of the obstacles 

 which have been laised against it. 



The greatest olistacle is the fact of a|H>siH>ry in Mo-sse-s. This 

 deywrture from ihe usual alternation will be more generally dis- 

 cussetl in -relation to the l'"erns, where it is more frequent. 

 Besides its iH'ing arlilicially imhiced in Mosses by special treat- 

 ment, it appears also to have been noted by I'go Unti in nature, 

 in Ihe case of atrophied capsules of /•'««,i//ii, which had buried 

 themselves in the soil. The es.sential (Hiint is the production of 

 the sexual generation by direct vegetative growth from the 

 neiitr^rl. This wi«ild appear to involve a reduction of chromo- 

 somes, but Tringsheim's drawings show nothing analogous to 

 Ihe usual process ol tetnvd division to form the spores ; the 

 reduction, if it occurs, must be elVected in some other way. 



.•\ the»>relical suggestion on this (xiint will be made later. 

 Meanwhile let us eslimaie its prolvible imixirtance as reganls the 

 Hryophyla. It cannot fail to strike the ol>server how unilorm 

 is the alternalion ii\ these plants : there are, 1 lielieve. no 

 recorded Ci\seii of deviation fronr the normal alternation in 

 Liverworts. 1 know of only a single case of aixispory among 

 Masses taken in the open, and then in atrophial ca|)sules; 

 apivs|H>ry, when imUlced, follows such extreme treatment as 

 chopping the sivrogoniuin into pieces. .\nil it is not as if the 

 Mivsjies and I.iveiworts had e.scafxxl detailed ol>servation ; 



NO. 151;. VOL. 59] 



hardly any group of plants had been more carefully cxamiiud 

 by coiinietent observers. Deviations from strict nltcrnaiiin 

 then are rare, and appear under physiologicol stress. Tlii^ 

 great groui), which includes the simplest spoiophytcs among 

 Archegoniale plants, is also singularly constant in its alternation. 

 I think Ibis is to be cimnected with the permanently dependent 

 condiiion of the sporophyte; its equable physiological con- 

 dition, nursed and protected by the Moss j>lant, Ihids its 

 morphological expression in its comparative uniformity. Con- 

 versely the independent position of the siiorophyle in Kerns, and 

 its exposure to varied conditions may have cliiileil more freely 

 in them unusual ilevelopments. 



III. .■l/'iiorma/ifi<s. 

 .■\nil now 1 may pass to my third point, and discuss more 

 geueially tlu- .iigumenl from abnormalities. I have no wish to 

 prejudge the ipusiion by the use of this term as applied to 

 apogainy aiul apospory, or in any w.iy to detract from their 

 morphological importance — I merely intend to express that they 

 aie departures Irom that order of events which is the most 

 fre(|ueiu in .\rchegoniate plants at large, and I particularly wish 

 to point out that while such irregular developments are now 

 shown to be frequent in Kerns, they are exceedingly rare in 

 Uryophytes, and are not, I believe, hitherto recorded lor Lycopo- 

 dineae or Kquisetineae. 



While direct vegetative transitions from one generation to the 

 other may appear as a /r/'w/.i /ii<7V support of an homologous 

 origin ol the two generations, 1 must protest against their being 

 used, as they have been, as evidence against an antithetic view. 

 It has been said that the facility with which these transitions 

 from one generation to another in Kerns take place " shows that 

 there is no such bard and fast distinction between the generations 

 as the antithetic theory would appear to demand." Why should 

 it demand a hard and fast distinction ? Kor my own part, I 

 had already described apogamy and apospory as occurring in the 

 same individual belore I wrote on alternation. The presumption 

 seems to be that a distinct course of evolution must have im- 

 posed " hard and fast " limits upon the potentialities of the parts 

 evolvcil. Hut we ought to remember how the root, whether in 

 I'hanei ogams or l-'erns, has doubtless had a long course of 

 evolution as a mendier distinct from the shoot ; and yet we see 

 it bearing adventitious buds upon it, as in the Rosaceae, I'oplar 

 or Khn ; or even tr.msl'ormed at its ajiex into a shoot, as in 

 Pliilyctrium M Anl/iiiriiiiH. Such cases as these, though not 

 exact |vanillels, should sullice to show that hard and fast lines 

 are not to be anticiimted as a consequence of a distinct course of 

 evolution. 



There is another kindred, though almost converse, proposition 

 which has been advanced by I'ringsheim. lie made his ex- 

 periments on Moss fruits, " in the hope that he would succeed 

 in producing protonema from the subdivided seta of the Mos.ses, 

 aiHi thus prove the morphological agreement of seta and Moss- 

 stem." The point here appears to be that parts which are 

 cajwble 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 conversion ol their apices into shoots, does not prove their 

 "morphological agreement" with shoots upon which such 

 developments are comnron. 



Hy those wlu> use such arguments it is to be Ixirne in mind 

 that the two generations, however distinct in their evolution, 

 are still merely stages in Ihe life-history of one and the same 

 organism. Tlie 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 vaiious ^loten- 

 tialities come into evidence, as, for instance, in the formation ol 

 an apogamous sporophyte, or of an ap<.isporous protonema : hut 

 that sonie such potentialities aie there is in no way inconsistent 

 with the antithetic theory. 



I have above pointed out how morphology has recently passed 

 to an experimental stage, and I am glad to stry that by means of 

 the cultures of Or. Lang and others we are beginning to gain an 

 insight into the ciiciimstances which lead to >hese phenomena. 

 In certain Kerns direct apogamy occurs: that is, "the imme- 

 diate production ot vegetative buds by prothalli which are 

 u.siially incapable of being fertilised"; the origin of this is still 

 obiscure. Kut apogamy may also be inducei.1 in various other 

 si>ecies. V>(. Uing states that "the causes which appeared to 

 iniluce aixigainy in these prothalli were, the prevention of contact 

 with tUiid water, which rcnderetl fertilisixlion impossible, and 



