DARWIN'S ALTERNATIVE EXPLANATION OF EVOLUTION. 63 



by the fact that in deserts numerous " species " are recognized, of 

 genera growing elsewhere with conspicuous flowers, which have varied 

 into the cleistogamous state in the absence of insects.* 



The origin, therefore, of varieties is obviously self-adaptation to 

 new conditions of life. This corresponds with Darwin's " Definite 

 Variation." 



As an important result of the ecological method of studying plants, 

 it will be discovered that all the peculiarities of structure by which 

 Monocotyledons are distinguished from Dicotyledons can be correlated 

 with those of aquatic Dicotyledons ; so that the cumulative coinci- 

 dences prove inductively that the former class have been derived from 

 the latter. f Similarly it is a very probable inference that Dicotyledons 

 were derived from Gymnosperms ; but as the proof must come from 

 extinct plants, there are still important links which remain as yet 

 undiscovered, as the source of the ovary, style and stigma. 



Conclusion. — The few examples herein supplied can be multiplied 

 indefinitely ; but what I am anxious for the reader to remember is 

 that the long experience of cultivators and scientists, like Carriere 

 and Buckman in the 'sixties ; of scientists of to-day, as Schimper, 

 Costantin, and Warming, all agree in the same conclusion that 

 Darwin's alternative is "forced" upon everyone who will patiently 

 study Nature from his point of view. That conclusion, I repeat, 

 is, that the origin of altered structures — whether they be merely 

 temporary, or fixed and hereditary, and called varieties and species 

 by systematists — is, in every case, due to the power of plants to 

 respond to the direct action of changed conditions of life. J 



* I have described and figured several species in my paper on " The Origin 

 of Plant Structures by Self-Adaptation to the Environment, exemplified by 

 Desert or Xerophilous Plants " (Journ. Linn. Soc. Bot. vol. xxx. p. 218, 1893). 



t Journ; Linn. Soc. vol: xxix. p.' 485 (1892) ; and Ann: Bot: vol. xxv: (191 1). 



% M. Costantin observes : " Nous sommes amenes a penser, pour ainsi 

 dire invinciblement, que Ton ne peut expliquer les caracteres generaux des plantes 

 arctiques que par une adaptation. Si toutes les plantes arctiques sont vivaces, 

 c'est parce qu'elles vivent au voisinage du pdle " (Les Vigetaux et les Milieux 

 cosmiques (Adaptation — Evolution), 1898). 



