i8 4 SCIENCE PROGRESS. 



in this field especially, been added to our store of know- 

 ledge that the enumeration of a few cases must suffice, 

 e.g., Epiphytes, 1 succulents, 2 mangrove-vegetation, 3 aquatic 

 plants, 4 climbing plants, 5 etc. 



I will now briefly review the various theories of adap- 

 tation which have been put forward. This can only be 

 done briefly, as a more detailed account would take up a 

 whole book. 



The best known and most familiar theory of adapta- 

 tion is that of Darwin. In the main his theory is one of 

 ''the survival of the fittest". He attaches a certain, 

 though somewhat slight, importance to the conditions of 

 life, and to the effects of the use or disuse of organs. 

 Hence it is clear, however, that, regarded from this point 

 of view, the question is not so much one of how plants 

 become adapted, as the selection of those which have be- 

 come adapted. For adaptation clearly means that the 

 organs possess the faculty of changing their structure and 

 form by the influence of external conditions. That, 

 within certain limits, this power is inherent in plants, 

 nobody doubts, but the question is, whether organic con- 

 ditions which have become hereditary can originate in 

 this way. Nageli's 6 theory of adaptation distinguishes 

 between two kinds of changes which take place under 

 external influences : temporary changes, which only last 

 as long as their cause, and lasting changes, which con- 



1 Schimper, die epiphytische Vegetation Americas (Bot. MittheiL 

 aus den Tropen), Goebel, Prlanzenbiol, Schilderungen. 



2 Goebel, ibid. 



3 Goebel ibid., Schimper, /. c. ; Karsten, Die mangrove vegetation 

 (Bib/iot/ieea botanica). 



4 Goebel, Schilderungen, ii. ; Schenk, Die Biologie der Wasserge- 

 wachse, Bonn, 1887. 



5 Treub, Sur une nouvelle categorie de plantes grimpantes, and 

 Observations sur les plantes grimpantes du jardin botanique de Buiten- 

 zorg, Annates du j. b. de Buitenzorg, vol. iii. Schenk, Lianen, in Botan. 

 MittheiL a. d. Tropen, iii., iv. 



6 Nageli, Mechanische Physiologische Theorie der Abstammungs- 

 lehre, 1884. 



