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developments in piiyla. vvliich are believed to have been of distiiat origin ' - is 

 even more significant. Professor Bower spoke of the prevalence of this as an 

 'obstacle to success/ and so it is if our aim is purely pliyletic. In another way 

 the demonstration of parallel developments constitutes a positive result of great 

 value. Thus Professor Bower's own work has led to tlie recognition of a number 

 of series leading from the lower to the higher Filicales. By independent but 

 parallel evolutionary paths, from diverse starting-points in the more ancient 

 Ferns, such similarity has been reached that systematists have placed the 

 plants of distinct origin in the same genus. In these progressions a number of 

 characters run more or less clearly parallel, so that the final result appears to 

 be due ' to a phyletic drift that may have affected similarly a plurality of lines 

 of descent.' This conclusion, based on detailed investigation, appears to me to 

 be of fai'-reaching importance. If a ' phyletic drift ' in the Ferns lias resulted 

 in the independent and parallel origin of eucli characters as dictyostely, the 

 mixed sorus, and the very definite type of sporangium with a vertical annulus 

 and transverse dehiscence, the case for parallel developments in other groups is 

 greatly strengthened. The interest shifts to the causes underlying such progres- 

 sive changes as appear in parallel developments, and the problem becomes one 

 of causal morphology rather than purely historical. 



The study of parallel developments would, indeed, seem likely to throw 

 more light on the morphology of plants than the changes traced in a pure 

 phyletic line, for it leads us to seek for common causes, whether internal or 

 external. We cease to be limited in our comparisons by actual relationship, 

 or forbidden to elucidate the organisation in one grouj) by that which has arisen 

 independently in another. Similarly the prohibition against comparing the one 

 generation in the life-cycle with the other falls to the ground, quite apart from 

 any question of whether the alternation is homologous or antithetic. The 

 methods of advance ' and the causal factors concerned become the important 

 things, and if, for example, light is thrown on the organisation of the fern-plant 

 by comparison with the gametophyte of the moss, so much the better. This, 

 ho\yever, is frankly to abandon phylogeny as ' the only real basis of morpho- 

 logical study '^ and with this any attempt to base homology on honiogeny. Many 

 of the homologies that exist between series of parallel development are what 

 have been happily termed homologies of organisation ; these are sometimes so 

 close as to result in practical identity, at other times so distinct as to be 

 evident homoplasies. The critical study of homologies of organisation over as 

 wide an area as possible becomes of primary interest and importance. 



Since about the beginning of the present century a change of attitude tcnvai-ds 

 morphological problems has become more and more evident in several ways. 

 It seems to be a phyletic drift affecting simultaneously a plurality of lines of 

 thought. _ The increasing tendency to look upon problems of development and 

 construction from a causal standpoint is seen in the prominence given to what 

 may be termed developmental* physiology and also in what Goebel has called 

 Organography. = These deal with the same problems from different sides and 



^ This and other quotations in this paragraph are from Profeesor Bower's 

 address to Section K in Australia {Brit. Assoc Hep. 1914). 



^ In this connection it is of interest to remember that Professor Bower has 

 always laid stress on the importance of studying methods of advance and has 

 regarded in this way examples which some other morphologists have used to 

 form an actual series. His use of the bryophyte sporogonium in explaining 

 the origin of the sporophyte is a casei in point. (Ci. Annals of Botany, vol. viii., 

 p. 344.) 



* Strasburger, Text Book of Botamj, p. 9. It would be truer to say that 

 morphology has been the basis of phylogeny. If each is to be the basis of the 

 other, the building can hardly progress ! 



° The special meaning attached by Goebel to Organography is difficult to 

 ascertain and has undergone a fundamental change between the first and second 

 editions of the AUgcmcine Oigunoijraphle. In the second edition (p. 8) the 

 dependence of construction on function is regarded as open to question and in 

 specific cases as untenable (p. 39). The justification for an Organography 

 instead of a General Morphology would thus really disappear. 



