668 



GA RDENERS* MA GA Z/NE. 



October i 5i ^ 



Homology of Plants. 



• By Professor F. 0. Bower, D.Sc, F.R.S. 



( Continued from page 653. ) 



III.— Abnormalities. 



And now I imay pass to my third point, and discuss more generally 

 the argument 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 Lycopodine;e or Equisetinea^. 



While direct vegetative transitions from one generation to the other 

 may appear as a 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 antithetic 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 that a distinct course of evolution must have imposed "hard and 

 fast" limits upon the potentialities of the parts evolved. But we ought 

 to rember 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 Rosacea?, Poplar 

 or Elm ; or even transformed at its apex into a shoot, as in Platycerium 

 or Antkuriunu 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. He made his experiments on Moss 

 fruits, "in the hope that he would succeed in producing protonema from 

 the sub-divided seta of the Messes, 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 " morpho- 

 logical 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 such 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, 

 qualities of the race 



were all cultivated under artificial conditions and arT^T ^ " 



shade-loving plants, a habit which must affect their nnfv acteristic ally 



.t • ~« — 1 . mcir nutrition. p e rK 



the most interesting case, nowever, is that described k\ a 1 . mh *P> 

 Onoclea. In plants from which, by removal of the f T ^ S() n in 

 sporophylls had been induced to change their chararte 86 lhe 

 as foliage leaves, the son were arrested. "When the 1 f! evelo P 

 much of its reproductive function that the sporangia a r J T'° St . S0 

 rare or rudimentary in the sorus, aposporv frennenth, ^ Dec <>niii^ 

 placenta develops amon* the rudir^ 



The heredit.u y 



as a whole must be transmitted through the 



It may be a question how far, and under what 



various potentialities come into evidence, as. for 

 instance, in the formation of an 



successive generations, 

 conditions, its 



ftpogamous sporophyte, or of an 



aposporous protonema ; but that some such potentialities are 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 say that by means of the cultures 

 ot Dr. Lang and others we are beginning to gain an insight into the 

 circumstances which lead to these phenomena. In certain Ferns direct 

 apogamy occurs ; that! s, the immediate production of vegetative buds 



placenta develops among the rudimentary snnranma i — 

 growths." Here is, again, a case of deficient nutrition fht £^? Mi 

 leaves, after formation, but before they could have c ■ ? ng 

 functions far, were removed. The plant makes an effort to Tuonlv ^ 

 place at the expense of spore production ; arrest of sori and SI • 

 is the result, accompanied by cases of the direct vegetative tiw^' a 

 to the prothallus. From these examples we see thlrSdeS I 

 least, disturbed nutrition is frequently, perhaps always, a concomitant ?r 

 apospory. Thus there is some countenance for the view that ani™ 

 and apogamy follow on converse conditions of nutrition F us >pory 



We may next inquire how these converse conditions may lead to 

 changes in question ; and especially the stale of the nuclei ought to 

 be considered Owing to practical difficulties of observation the 

 behaviour of the nuclei in apogamy and apospory has not been 

 directly followed. But if the nuclear difference between the two genet a 

 tions be, as it is believed, nuclear changes will be closely connected with 



^^^^ -a A a M M ■ A 



appear more natural than that 

 apogamy, which presumably involves a doubling of the chromosome* 

 should follow a condition of plethora, and that apospory, which pre' 

 sumably involves a halving of the chromosomes, should follow deficient 

 nutrition ? 



One further fact in either case appears to me to be specially note- 

 worthy, that the changes are not confined to a single cell. The directly 

 apogamous bud of Lastrea fitix-mas may, perhaps, be referable to 

 a single cell, but Dr. Lang shows by numerous examples that the transi- 

 tion from characteristic tissue of the gametophyte to that of the sporo- 

 phyte may arise at various points, and involve considerable tracts of 

 tissue. Similarly I have shown in the case of apospory that the change 

 may affect not one cell only, but cell-groups at various and distinct points 

 of the same individual. It would seem that there is a widespread dis- 

 position of the tissues to undergo the change. 



For my own part, I think the usual attitude on the chromosome ques- 

 tion has been too absolute and arithmetical. Evidence is accumulating 

 from various sources that the usual numbers are not strictly maintained ; 

 it is known that in vegetative cells there are often considerable differ- 

 ences of the number of chromosomes from those in the sexual cells of 

 the same plant, while observers have noted the irregularities in the divi- 

 sions of the pollen-mother cells in such plants as Hcmerocallis and 

 Tradescantia. If there be any causal connection between the number of 

 chromosomes and the morphological character of the sporophyte ai 

 gametophyte, irregularities such as these at least countenance the idea of 

 nuclear instability being possible. It will be a question for special treat- 

 ment and investigation how far nuclear instability is connected with dis- 

 turbed nutrition. But into the mechanism of the presumable nuclear 

 change, and the question whether it be sudden or gradual, we cannot enter 

 with any more than a speculative interest, in the absence of direct ob- 

 servations. Whatever the nuclear details may be, I regard it as a matter 

 of very great importance to recognise that special conditions of nutrition 

 commonly accompany, if indeed they do not actually determine, those 

 changes which we term apospory and apogamy. But the story of the 



bv nrothalli whirh ar* ,k nil,; J T A • •,• 7f ia , uvc U . U V S <~»<*"geb wnicn we term apospory and apogamy. Jt>ut tne story 01 mc 



of his is s il7o bscurP > X apaUe ° f be / ng / ert . ll ' sed *J .^e origin past is not simply a matter of conditions of nutrkion, as we see them now 

 or tms is still obscure. But apogamy may also be induced in various influencing- Arrhecmni^ «i*«*c &* w «p n t h\!rh\v «™>r\a\\*ed state. 



. ^ — apogamy may 

 other species. Dr. Lang states that " the causes which appeared to 

 induce apogamy in these prothalli were, the prevention of contact with 

 fluid water which rendered fertilisation impossible, and the exposure to 

 direct sunlight. Possibly the temperature had some effect." It is 



fur her to be noted that in every case of induced apogamy "normal 

 embryo 5 «""■'> *mJ»»<< — «- — — • •-- - ■•■ ■ 



influencing Archegoniate plants in their present highly specialised state. 

 The real question is a purely historical one, How did the present state of 



things come about ? 



( To be continued. ) 



the conditions of 



Now 



... , , . , prevention of fertilisation, exposure to light, and 

 possibly also a high temperature, all lead to a plethoric state, which we 

 may thus recognise as a precursor of induced apogamy, possibly also of 

 apogamy at large. 3 



On the other hand, the circumstances which precede or accompany 

 apospory are commonly those of deficient nutrition. In the case of Ugo 

 i>ruis l< loiana, it is mentioned that the capsules were atrophied and 

 buried in the soil, where they could not obtain nourishment by their own 

 assimilation. In the induced apospory of Stahl and Pringsheim the 

 growths appear upon parts of the chopped up seta, isolated from their 

 usual sources of supply. Among Ferns, the conditions of nutrition 

 which precede apospory have not been noted in all cases ; but the follow- 

 ing tacts are {interesting. Athyrium fdix-famina var. darissima is a 

 paie cniorottc *ern with exiguous leafage, while the more or less com- 

 plete arrest of the sporangia is a concomitant of apospory. In Poly, 

 stu/ium angulare var. pulcherrimum there is no obvious disturbance of 

 he vegetative organs, but I have specially noted the sporal arrest, which, 

 hi ' PeC "" enS examined by me, appeared to be complete. This is, 

 S fc COIKOm . ,tant of apospory, though it may be uncertain how far 



bor on Tf th. ^PO'y: this is accompanied by 

 abortion of the sporangia, though some 



stages of 



Centennial Qrape When Messrs. T. Rivers and Sons recently exhibited 



fruit of this Australian white grape the berries, long oval in shape, were the largest, 

 perhaps, of any white variety seen. Not only were they devoid of quality, but 

 were, on being cut, found to be hollow. Possibly the variety had in that case 

 been too liberally grown and fed. Mr. W. Roupell had a small bunch of the 

 variety at the Drill I lall on the 20th ult„and the berries, smaller and better coloured 

 though still very fine, were of far superior quality, having firm flesh of a ncfl 

 musky flavour. It had all the appearance in that case of being a big Cannon liaii 

 Muscat. Mr. Roupell had found it to be like that variety, an indifferent setter. 

 I hs Diamant Traube, a pretty white grape, which he strongly recommended tor 

 invalids, merits all his praise for such purpose.— A. D. 



Park Place, Henley on Thames.— That a most enjoyable day is spent at 

 the above place on the occasion of the annual reunion of past and present empl")" 

 is proved by the large number of old hands who availed themselves of Mrs. JNowe s 

 kind hospUahty un a recent occasion. The invite extends to all who have servea 

 in the gardens or on the estate during the last twenty-five years, and many are w 

 happy meetings of men who served together in bygone days, and whootnerug 

 would seldom or never come into contact with each other again. The mho » 

 interest evinced by Mrs. Noble in the welfare of all who have served on ne 

 beautiful estate is sincere, and her presence on the scene of the days 

 hailed with the warmest enthusiasm by all. An interesting ramble round the 

 kept gardens and grounds with the able and respected chief, Mr. G. Sumo 

 under whom a 1 have served, occupies the early part of the day, and la te c n» 

 match is played between past and present members of the club, the latter »nw»°2 



showed apospory 



nad been raised bv Mr I nu»r a ^pory at so peculiarly eany a stage 



divided, a process calculated to Tec?^*^^ ^ ^J?^ 1 * 

 -posporous plants of Trickon^ltl P ^!!?fci 2# ' 



Ift 



played between past and present members of the club, the latter invar' 



„ the game. It must be very gratifying to Mr. Stanton to have a ™ un " 



so many of nis old men now away and occupying good positions m various par 

 of the country-men, too, who owe much to the teaching of their maste t, 

 L P wf a "!f" erS and in botany lessons, which were ; given in spare time 

 £ J? y ^»«»dside and meadow rambles. Gardeners do not, as * r , 

 have too many holidays, but this is one most keenly enjoyed by 

 SKft SS °- C Cannot hel P linking how many might spend enjoya We days 



w if i ? enngs t0 toke phce on the manv lar i estates throu e hout 1 



