io6 



NATURE 



[September 24, 19 14 



in a different way, as indeed many workers have 

 already been doing. To start, not from preconceptions 

 based upon limited pala;ontological data, but from an 

 intensive study of the living plants themselves. To 

 widen so far as possible the criteria of comparison, 

 by making, for instance, every possible use of cellular, 

 physiologico-chemical, and especially secretory detail, 

 and of minor formal features, such as the dermal 

 appendages, or by initiating a new developmental 

 morphology of the flower from the point of view of 

 its function as a whole : and with its physiological 

 end clearly in sight, viz. the maturing, nourishing, 

 and placing of new germs. To make on some such 

 basis intra-ordinal, and intra-generic comparisons with 

 a view to the phyletic sanation of closely related 

 forms ; and so to construct probable short series, which 

 may subsequently be associated into larger phyletic 

 groupings. This should be checked wherever possible 

 by physiological probability. A keen eye should be 

 kept upon such information as geographical distribu- 

 tion and palaeontology may afford, and especially upon 

 the fossils of the Mesozoic period. What is above all 

 needed for success among the Angiosperms is new 

 •criteria of comparison, to meet the far-reaching diffi- 

 culties that follow from parallel development and 

 recent adaptation. If some such methods be adopted, 

 and strenuously pressed forward, the task should not 

 .appear hopeless, though it cannot be anything else 

 than an arduous one. 



I cannot conclude without some remark on the 

 bearing of parallel or convergent development, so 

 fully exemplified in the Filicales, upon the question 

 of the genesis of new forms. Anyone who examines, 

 from the point of view suggested in this address, the 

 larger and well-represented divisions of the Vegetable 

 Kingdom must be impressed with the extraordinary 

 dead level of type to which their representatives have 

 attained. In most of these divisions the phyletic his- 

 tory is obscured, partly by the absence of any consecu- 

 tive palaeontological record, but chiefly by the want 

 of recognised criteria for their comparison. This is 

 very prominently the case for the Mosses, and the 

 Angiosperms. 



But it may be doubted whether these large groups 

 iiiffer in any essential point, in respect of the genesis 

 of their multitudinous similar forms, from the Fili- 

 cales, in which the lines of descent are becoming 

 clearer through additional knowledge. Suppose that 

 w^e knew of no fossil Ferns ; and that none of the early 

 fern-types included under the term " Simplices " had 

 survived in our living flora : and that the Filicales of 

 our study consisted only of the 2500 living species of 

 the old undivided genera of Polypodium, Asplenium, 

 Aspidium, and Acrostichum. Then the phyletic pro- 

 hlem of the Filicales would appear as obscure as does 

 that of the Mosses, or of the Angiosperms of the 

 present day. They would present, as these great 

 groups now do, an apparent dead level of sameness in 

 type, though the phyletic starting-points in each may 

 have been several and distinct. There is every reason 

 to suppose that in the phylesis of the Mosses or the 

 .-\ngiosperms also there has been a parallel, and even 

 a convergent, development of the same nature as that 

 which can be cogently traced in the Filicales : but 

 that it is obscured by the obliteration of the early 

 stages. Internal evidence from their comparative 

 study fully justifies this conclusion. How, then, are 

 we to regard this insistent problem of parallelism and 

 convergence from the point of view of genetic study? 



A belief in the "inheritance of acquired characters," 

 or, as is sometimes expressed, "somatic inheritance," 

 IS at present out of fashion in some quarters. But 

 though powerful voices may seem to have forced it 



NO. 2343, VOL. 94] 



for the moment into the background, I would take 

 leave to point out that such inheritance has not been 

 disproved. All that has been done, so far as I under- 

 stand the position, is to show that the evidence 

 hitherto advanced in support of it is insufficient for a 

 positive demonstration. That is a very different thing 

 from proving the negative. We hear of " fluctuating 

 variations" as distinct from "mutations"; and it is 

 asserted that the former are somatic, and are not in- 

 herited, while the latter are inherited. This may be 

 held as a useful terminological distinction, in so far 

 as it accentuates a difference in the heritable quality. 

 But it leaves the question of the origin of these herit- 

 able "mutations" quite open. At the present moment 

 I believe that actual knowledge on this point is very 

 like a complete blank. Further, it leaves indefinite 

 the relative extent and proportion of the "mutations." 

 It is commonly held that mutations are considerable 

 deviations from type I am not aware that there is 

 any sufficient ground for such a view. It may probably 

 have originated from the fact that the largest are 

 most readily observed and recognised as reappearing 

 in the offspring. But this is no justification for ignor- 

 ing the possibility of all grades of size or importance 

 of heritable deviations from type. 



On the other hand, adaptation, w'th its consequence 

 of parallel or even convergent development in distinct 

 stocks, is an insistent problem. The real question is : 

 What causes are at work to produce such results? 

 They are usually set down to the selection of favour- 

 able divergences from type out of those produced at 

 random. But the prevalence of parallelism and con- 

 vergence suggests that those inheritable variations, 

 which are now styled "mutations," are not produced 

 at random. These facts enforce the question whether 

 or not they are promoted and actually determined in 

 their direction, or their number, or their quality, in 

 some way, by the external conditions. Parallelism 

 and convergence in phyletic lines which are certainly 

 distinct impress the probability that they are. Until 

 the contrary is proved it would, in my opinion, be 

 wiser to entertain some such view as a working hypo- 

 thesis than positively to deny it. Such a working 

 hypothesis as this is not exactly the same as a 

 " mnemic theory," though it is closely akin to it. It 

 may perhaps be regarded as the morphologist's pre- 

 sentation, while the mnemic theory is rather that of 

 the physiologist. But the underlying idea is the same, 

 viz. that the impress of external circumstance cannot 

 properly be ruled out in the genesis of inheritable 

 characters, simply because up to the present date no 

 definite case of inheritance of observable characters 

 acquired in the individual lifetime has been demon- 

 strated. Of course, I am aware that to many this is 

 flat heresy. At this meeting of the Association it 

 amounts almost to high treason. I plead guilty to 

 this heresy, which may by any sudden turn of observa- 

 tion be transformed into the true faith. I share it in 

 whole or in part with many botanists, with men who 

 have lived their lives in the atmosphere of experi- 

 ment and observation found in large botanic gardens, 

 and not least with a former President of the British 

 Association, viz. Sir Francis Darwin. 



It is noteworthy how large a number of botanists 

 dissent from any absolute negation of the influence of 

 the environment upon the genesis of heritable char- 

 acters. Partly this may be due to a sense of the 

 want of cogenc\- of the argument that the insufficiency 

 of the positive evidence hitherto adduced justifies the 

 full negative statement. But I think it finds its real 

 origin in the fact that in plants the generative cells 

 are not segregated early from the somatic. In this 

 respect they differ widely from that early segregation 



