September 24, 1898. 



GARDENERS' 



MAGAZINE. 



621 



es must still be open for discussion. It is a tenable view that the 

 hie phyla arose separately from a nonfoliar ancestry, and that the 

 sumption of a foliar development, having in each case a different habit, 

 nH a different relation to the sporangia, led to the distinctiveness of 



tTnuous at^^l ™ \? a m « tam . or P hosis of a strobilus > which had a con- 

 some of these Md repetition of sporophylls, but that 



StfJw^r^, 0 ' thdr s P oran S ia » with the correlative 

 fw «I.fi "? e fW alIve development. A differentiation of the strobilus 



g&Z^O^n^^k homology bT d7scen7of the TOSSSTSSTS n A a d iffe ^fon of the strobilus 



Ives of these PteriSophyta must at pr.sent remain in suspense ; but the sterilisation of ,™fflk T^iLla^"*"" 1 ° f f ° hage le ^ CS S y 

 5Tf. SwESnt with the leaf of Pteridophvtes as compared with the leaf protophvlls oriCR.. *™ g ™ ng ft* SOm * ma T su ^st that the 



'eaves 01 tnese ricnuupuvia ujuji at -ocm itma»» »*• — t^*— »r , 

 case is different with the leaf of Pteridophytes as compared with the leaf 

 of Bryophytes ; unless the whole morphological system of the time be in 

 error, we shall be right in maintaining that these foliar developments 

 have been distinct in origin from the first. 



Xow all the foliar parts above quoted would in a system of merely 

 formal morphology fall into the category of " leaves." But if phylogeny 

 be accepted as the only real basis of morphology, we must be prepared 

 to split up the category based on mere time, place, and mode of origin, 

 and to recognise in some cases repetition of individual parts ; in others 

 essential correspondence, but not individual repetition, owing sometimes 

 to transfer of developmental capability ; in other cases, again, a possi- 

 bility of distinct origin by descent not actually proved; and, lastly, a 

 reasonable certainty of distinct origin. The practical question for the 

 morphologist is, having recognised these facts for himself, how is the 

 matter to be best made intelligible to others ? 



A reconsideration of the term " homology * will thus be necessary : is 

 it to be applied equally to such parts as are connected by lineal descent, 

 and also to those which we have good reason to believe have resulted 

 from parallel development in quite distinct phyla ? Or, to put a finer 

 point upon our inquiry, are we to distinguish in any way the cases of 

 ■ individual repetition " from those of "essential correspondence"? In 

 the latter case I think no good end would be served at present by accen- 

 tuating this distinction by terms, the steps of divergence are so slight 

 and gradual None the less should it be clearly borne in mind that com- 



ft?s ^ on ^ d «> the same way. It is possible that they did ; but 



thinnl P n SS K ft a \ d ' b View ° f the P eculiar case of Phylloglossum, 

 olastir H^f Pr ° bable Z that in these P lants we have an example & horned 

 two stilf ^ P r nt D °/ ?, art ? distinct as to descent > while the limits of the 

 Zl» 5 t 1 i m Ph yl l °£ lossi <™ became obliterated in the more complex 



^nncfiKf f °*T- The P roof of the P° int wil1 be diffi cult or even 

 impossible, but the eyes of botanists should certainly be open to recog- 



?/? e a ! uch .! nd k lv ' du ^ | nomopIasy f should it occur, and to inquire whether 

 it has really had a place in plant-development. 



Returning now to homoplastic development in distinct groups of 

 plants, the morphology of the foot provides interesting material for'com- 

 parison, and especially so since there is no question of repetition here ; 

 tor the comparison is between parts cf which only one appears on each 

 individual plant. 



The term foot has been applied to that part of the embryo in 

 r'teridophyta which serves to connect it physiologically with the pro- 

 tnallus ; the term has also been used for the base of the seta in 

 Bryophytes. Parts performing a similar function, but not referable as in 

 other Phanerogams to the metamorphosis of cotyledons, are also found in 

 Gnetum and Welwihchia. 



In the Bryophyta what is usually called the foot is no definitely 

 specialised structure ; it is merely the absorbent base of the seta. It 

 would appear probable that in the Bryophyta a true homogeny holds in 

 all cases, as the requirement for it will have been uniform ; and its 



^ *_» — ' ■ *»• p-»"ww»ww**.»^ mm w m mm ■ ■ w * a w will 7 W * ■ J * V-/ I l v TT 111 Mil V V. i ) \X\\\X\j\ 111 i I I i V i Lw 



parisons of parts commonly ranked as homologous in the plant body are basal position is also uniform, though some difference of detail does 

 based on a less complete individual correspondence than that of parts ™ " ' ' ' ' 



usually compared in the animal body. 



But the case is different in dealing with parallel developments, and 



some doubt arises whether parts which probably, or it may be certainly, 

 have arisen by separate evolutionary sequence in distinct phyla are to be 

 classed as homologous in the same sense as those directly related by 

 descent. This question was long ago taken up on the zoological side by 

 Professor Ray Lankester, and it was shown thatj t the old word 

 homology » covered two things recognised as distinct from the point of 

 view of descent. He defined as homogenous " structures which are 

 genetically related, in so far as they have a single representative in a 

 common ancestor." On the other hand, "when identical or nearly 

 similar forces or environments act on two or more parts of an organism 

 which are exactly or nearly alike : further, if, instead of similar parts in 

 ine same organism, we suppose the same forces to act on parts in two 



i - partS are exactl y or near 'y alike > and sometimes homo- 

 genetic, the resulting correspondences called forth in the several parts in 



STl lTKi« 01 ?- a !V SI ? S wil1 130 or exactly alike. . . . I propose to 



bnrtinn TT ° f a £ reement homdpiasis, or homoplasy." Now this dis- 

 am ,n,n . ter , ms L rec l l ? ,res a,so to be observed in plant-morphology, and 

 weLvp fn? that * has never yet been adopted byjbotanists, though 

 Itw^^ CaSC ^ ° f parallel dev e!opment. I do Aot pro- 

 take the ^£i P< i ! me J in assi S nin g these terms to familiar cases, but, to 



appear in the relation of this absorbing body to the first segmentations 

 of the embryo. 



In the Pteridophyta it is exceedingly difficult to be sure of the cor- 

 respondence by the descent of the foot in distinct types, and indeed it 

 should not be assumed that a specialised absorbent organ was always 

 present, though general surface-absorption will naturally have taken place 

 in all archegoniate embryos; indeed, the condition of some upright 

 embryos is such that a foot would never have been described were it not 

 for comparison with other types. In lujuisetum, fso<tes, Botrychium 

 all forms without a suspensor, and with an upright growing embryo — the 

 hypobasal half of the embryo, with or without a root, is absorbent as in 

 the Bryophyta, and is described as a foot ; it is quite possible to sec in 

 them the continuation of a primitive absorbent organ. This may also be 

 the case in the Marattiace;e, and it is specially noted by Campbell that 

 " in Marat tia ail the superficial cells of the central region become enlarged 

 and act as absorbent cells for the nourishment of the embryo." From 

 such types we may imagine the more specialised foot of the Leptospo- 

 rangiate ferns to have been derived by a localisation of the absorbent 

 function on one side only, which would be a natural consequence of the 

 embryo taking a prone, in place of the vertical position. 



A different course of events probably occurred in the Lycopodineae. 

 I am disposed to think that here the suspensor represents nothing more 

 than a specialised part of the primitive absorbent organ ; this seems to be 

 indicated bv the details as shown in Treub's figures of ccrnuum and 



take thp i — , . ^"Snmg mese terms toiammar cases, but, to r ,a ? a 'KT^Ta T% u r • nr — Z 2 V / j 



SflK f exa ?P les already cited, the leaf of a fern would be homoplastic indicated by the details as shown m I reubs figures of cernuum and 



moughnot homegenetic with the leaf of a moss - or taking examnles £ Phlegmxria, in whtch the suspensor is contnrapos with the foot. But 



fcr, Smore ne arly akin, it would appear To SS ibk\hat ?he leave? of what is then the "foot" of Sela^clla, which is quite apart from the 



ntanfc ° — r , • c ^ A > or > laKing examples 



the three dUHnrt "t*?* ^ lt would a PP ear P^sible that the leaves of 

 not !S£ tS!5S5/ ° f I,Vmg Pterid °P h y tes sh ™- merely homoplasy, 



hSLfS^ f0,ia ? e i eaves of most P ,ants are assumed in 



the 



But it is 



^dividual tnhT^ ? e J eaves 01 most P lants are assum< 

 quite a p 0 sihL ^ ^ ° f a ^ ere wpctitionfof development, uut it is 

 ^^^^e^^y n .^e plant-body (as is contemplated in the 



whethe! ?Sl SS hom °P las y may have had a pi 



tentheresu^ designate " leaves » have actually 



* r ^gards their Ar- . de y eI °P ment identical, or at least essentially similar 



numerous leave, 5 gm } * th ? race ' The P robler " is, given a plant with 

 fceir evolution T Va ^ u ? form and Unction, to unravel the real story of 



suspensor, the root intervening? On this point I think we obtain light 

 from Welwitschia and Gnetum^ for in these we see an absorptive organ 

 formed at a comparatively late period ; and it corresponds in position and 

 function though not in tin^e of origin or details of structure, with that of 

 Selaginella. I conclude that the 11 foot ,: of Selaginella is probably a later 

 fAfmotmn not mmnarable as regards descent either with the foot of 



We 



feede 



int. The latter 

 hows, and their 

 of the seed in 



evolution, f wc Tdktin.t f ♦ ™ n ™°n, to unravel the real story of 1Iuu ^i v with such structures as the pinme, stipules, indusium, corona, 

 «°>*°e even «S? tad!vid„ai aC vr- ay * COnttm P lated as mRSSi !T inconsun, *&.s k S Le^ncta and hairs 



i-Homogtny of -netirallv ' ^ - M when we speak of the -homologies; of these parts i rt is rarely the 



are plainly of recent independent origin as comparison i 

 actual position is defined according to the position 

 germination. Probably, then, there is homoplasy in such cases, not true 



homogeny. _ ..... 



Similarly with such structures as the pinna*, stipules, indusium, corona, 



. mi :»u airh inrnrtQtant hnrli^c a« #»m#»rt»^nrip<; and hair*; • 



thc Parts fbSd. ° f genetica "y related P arts » with or without repetition of 



** Reneticallv reUtL orig]I l of two or m ? re distinct categories of parts, 



w orkine un£ l' 0n the same or g an 'sm. 

 * !ite rating su?hS er . ?f these> and thus com Plicating the problem by 

 g^omenoii ofL/ ? t,nc ?° ns . as ma y hav e existed at first, may be the 

 If nition « iZi£Z 0r t» S ' S c- Th £ h t S late 'y received evolutionary 

 * here there has been I ? r - fesso r Goebe1 ' as restricted to those cases 

 , li °n accoumt °» v, o«s, change of function. We see how change 



be 



usually it 



position, or even in development and function, though not shown to be 

 comparable by descent. 



continued. 



of fun 



^at all w f vanous fo f ms of leaf ^ certain cases ; but it does 



m ^orphosi sof a Jinr , rmS • °" t , he Same p,ant were so Produced, by 

 The Lvconn?- g e or, & lnal type- 



K l & «^S B SrfSifS i f in illustration of this 

 !? "**r livint T ^ able Phyllog ossum is a more primitive type 



* ff «*nt form r K L y c °Pods; 



P5*^? thCSe ' a " 

 a Plant. ~kT_ are no 'ntermed 



*hich on ^nlro? ate J ste ? s betwee n them. This condition in 

 ferf'u 5 Mainly inters? groun J ds of comparison we believe to be primi- 



not arisen hv^ g '. and We , sha11 ask whether the two types of 

 ^Vodium there are. J. StmCt ev ?l ut,ona ry sequence? In the genus 



wtr 1atplv ... ... c are Certain snpriM «n.>, ^« T a— _t:-t. 0 _ft-_ 



'ines 



find 



•on *1 1? th at born 



ining 



tl ^at of pLn"i a s P? r °P h y»- When we compare this con- 



"yuogiossum it apears probable that the successive 



Autumn Sown Onions Vour correspondent M Lux 99 has fired at me be* 

 cause I have somewhat, in hii estimation, unduly trumpeted the meriti of the Ail» 

 C ' onion as I saw it both m an allotment and at a show, where thc bulbs 

 ^in a class for autumn sown onions easily at K; orn. Now, had these fine 

 buTbs been placed by N Teter " the trumpeting would have been all the other 

 wa V and readers of the GaRDENKRS Magazine would have been smothered in 

 the tremendous overflow of Luxian eloquence. Weil, I have a reason, for I wish 

 r d the very thing he suggests, that is, try and induce show committees to 

 h the terms of their class for autumn sown onions ; and thereby induce 

 cnange a u 0 tment holders to forego growing the all too speedily decaying 



cottagers ^ ^ instead such varieties as Ailsa Craig, Sutton's Ai, Cranston's 

 F^°\ ior Banbun- Cross, and other similar fine white and brown, round and 

 1 be varieties. Not only because these are quite as hardy, indeed, rather hardier, 

 ht \ V because they produce from autumn sowings very full bulbs that keep 

 U S hen ripe till the end of the year, and therefore are far more valuable for 

 domestic use or market sale than are bulbi that are ripe to-day and rotten 

 t orrow Where onions in July and August are, though very fine and handsome, 

 stilTerowing it must be admitted that they are far more worthy of approval than 

 bulbs that have done growing, and will not endue a month longer. — A. D. 



