102 Transactions. 



(3.) Each of these species originated by a mutation or sudden change 

 involving the introduction - of at least one quite new unit-character,* and 

 this must have happened at some period anterior to that of the drought, 

 not as a result of any such condition. Like other differential characters 

 in general, those induced by this mutation would be at first perfectly 

 useless (De Vries, 1912, p. 534), and the changed form would get its 

 advantage only by the chance of the occurrence of the drought. The 

 new character or characters then became useful ; but we must resist the 

 temptation to regard the useful character {e.g., the excessively thick and 

 coriaceous leaf or long thick roots of the xerophytic Ranunculi) as an 

 adaptation to the needs of the new external condition. 



(4.) As " adaptations " can in this case not be denied, it follows that 

 all the changes which are truly '•' adaptations " in these species are of the 

 nature of " fluctuations," and if any of them be cultivated under more 

 favourable conditions the " adaptations " will disappear ; the plant will 

 then retain only so much of its xerophytic character as it had at the 

 beginning of the drought, which gave it its initial advantage over others, 

 and which was the result of some previous mutation. Until each plant 

 of the community, therefore, has been so transplanted and tested it is 

 impossible for us to tell which of its characters ought, and which ought 

 not, to be regarded as differential specific characters ; and it follows that 

 the status of each is doubtful except where the plant has no near relatives 

 at all among existing plants. 



(5.) It is very improbable that the species of this community were all 

 produced in the early stages of the drought by mutation. It is assumed 

 " that the origin of new forms is not due to a hard struggle, but is promoted 

 by a luxuriant environment and by easy conditions of development " 

 (De Vries, 1912, p. 520). It is shown that a species (or genus) which is in 

 a " state of mutability " may produce whole groups of new forms, even 

 " swarms " (as in the case of Draha or Viola in Europe), though some- 

 times apparently such changes are only sporadic (p. 549). In this case it 

 must be supposed that at some more or less remote period before the 

 drought each of the genera Ranunculus, Lepidium, Oreomyrrhis, Myosotis, 

 and Poa passed through a " mutation period " and threw off numbers of 

 new species, some of which would immediately perish, while others would 

 maintain themselves for shorter or longer periods under the stress of 

 natural selection, and finally the species here perpetuated would alone 

 survive under the fierce stress of the drought until rejoined by their 

 relatives under the new climatic conditions: 



(6.) Narrowing down the proposition to the particular genus and species 

 here studied, we must believe that there existed at the beginning of the 

 period of drought a species (or possibly more than one) of Ranunculus 

 which had originated by mutation at some period (as to which it is useless 

 to speculate) having peculiarly thick leaves, long roots, and other characters 

 which gave it an advantage when the drought began to be severe. These 

 characters, however, had been acquired by it owing to causes which are 

 completely dark to us, not in response to any external stimulus or stress 

 of environment. Fortunate in possessing these characters, it continued 

 to live when other less-favoured Ranunculi perished, and it may or may 

 not have changed under the new conditions, adapting itself thereto. But 

 if it did so change it acquired no new unit- character ; and all its modifica- 

 tion remained mere " fluctuations," and under more favourable conditions 



* One is enough (De Vries, 1912, p. 562, in re Oenothera gigas). 



