PLANT MORPHOLOGY 79 



it will give way ultimately to the demands which a more detailed 

 knowledge of descent is sure to bring. 



It is well, however, in connection with discussions such as these, 

 to impress upon the lay public that all evolutionary theories are, like 

 other scientific theories, hypotheses incapable of complete proof. 

 No one will appreciate this more fully than biological investigators 

 themselves, for they are in the best position to know how insufficient 

 the evidence actually is, and how liberal a use has to be made of the 

 imagination in bridging over the wide gaps in the series of known 

 forms. The details of a story thus constructed depend so largely on 

 comparative opinion, and in so slight a degree on positive demon- 

 stration, that the history as told by competent experts in compara- 

 tive morphology may vary in material features. A little more weight 

 allowed for certain observed details, or a little less for others, will be 

 sufficient to disturb the balance of the evidence derived from a wide 

 area of fact, and consequently to distort the historical picture. There 

 is in truth no finality in discussions on the genesis and progress of 

 organic life, or in the kaleidoscopic changes of opinion, since any new 

 fact of importance will in some degree affect the weight accorded to 

 others, and may vary the general result. It will be objected that 

 conclusions which are so plastic are little better than expressions 

 of personal taste, that the study of comparative morphology is there- 

 fore calculated to dishearten its votaries, while the non-specialist 

 public, which is compelled to take its information at second hand, 

 will be bewildered, and will conclude that it is useless to pursue a 

 subject which shows so little stability. But on the other hand, those 

 who follow the progress of morphology with sympathetic care will 

 take heart when they compare its present position with that of a 

 generation ago; it is encouraging to think that it is little more than 

 half a century since the history of the life-cycle of a fern was first 

 completed. In some sixty years a vast array of kindred facts have 

 been acquired, and a theoretic structure is being raised upon them, 

 which, though still protean, is gradually acquiring some settled form. 

 Never has the advance of morphological thought been more rapid 

 than at present. The support of the facts of alternation from the 

 unexpected quarter of minute cytology has been one of the most 

 striking features in the recent history of our science. The discovery 

 of spermatozoids in the cycads and Ginkgoacece has filled in a gap 

 in the story of evolution, which all followers of Hofmeister must 

 have felt. But in no field of morphological research has investigation 

 been more amply rewarded than in palseophytology. The luminous 

 facts derived from fossils are shedding fresh light on obscure prob- 

 lems, such as the origin of the seed-habit, and helping us to locate 

 such difficult groups as the Psilotacece and Equisetacece. When we 

 regard these rapid advances, and truly estimate the influence they 



