416 Mr Patrick Geddes on ths 



On the Kahire and Causes of Variation in Plants."* 

 By Patrick Geddes, F.R.S.E. (Plate XIV.) 



(Read 8th July 1886.) 



While the fact of the origin of species by evolution is no 

 longer disputed, nor the operation of natural selection upon 

 organic forms any longer denied, the absence of any general 

 theory or rationale of variation in either the animal or the 

 vegetable world is not only generally admitted, but often 

 regarded as inevitable or even hopeless : variation to some 

 writers being simply "spontaneous" or "accidental"; to 

 others, if not fortuitous, at least dependent upon causes 

 lying as yet wholly, and perhaps hopelessly, beyond our 

 present powers of analysis. 



A theory of variation must deal alike with the origin of 

 specific distinctions and with those vaster differences which 

 characterise the larger groups. To commence, then, with 

 the latter, we may pose such questions as — 



1. How comes an axis to be arrested to form a flower? 



2. How is the evolution of the forms of inflorescence to 

 be accounted for ? 



3. How does perigyny or epigyny arise from hypogyny ? 



4. How is the reduction of the oophore and diflFerentia- 

 tion of the sporophore to be explained among cryptogams 

 and phanerogams, and why should the moss type be so 

 aberrant and so comparatively arrested ? 



5. How did angiosperms arise from gj^mnosperms ? 



6. How did wind-fertilised flowers arise ? 



7. How are the forms of fungi, algse, &c., to be explained? 

 Does the explanation of such questions really lie merely 



in the operation of natural selection upon innumerable 

 " accidental" variations requiring separate explanation in 

 every case, or is any constant law of variation discoverable? 



Let us note the parallelism of form exhibited in many 

 of these cases of unrelated organisms, and inquire whether 

 this does not give us some other clue to their origin. 



1. In phanerogams we find the raceme modified into the 



* A preliminary outline of a more extended analysis, underlying the writer's 

 essay on "Variation and Selection," in preparation for a forthcoming volume 

 of the Encydopcadia Britannica. 



A 



