DARWIN'S ALTERNATIVE EXPLANATION OF EVOLUTION: 59 



Ranunculus aquatilis Linn., with submerged dissected leaves, is 

 presumably descended from terrestrial species, as several other cases 

 occur, e.g. Helosciadium, Hottonia, &c, therefore induction suggests 

 that water is the cause. Mr. McCallum proved experimentally, by 

 adding nutritive salts to the water, how a similar plant (Proserpinaca 

 of the U.S.A.) was enabled to produce complete leaves under water. 

 Induction and experiment thus proved the fact that the " specific 

 character " of dissected foliage was caused by the direct action of 

 changed conditions of life (Darwin). 



It is also hereditary, for it is found to occur equally well when the 

 seed is sown in a garden border, and, as by Nature's experiment, when 

 a pond dries up, and it flourishes in the mud. 



Hygrophytes. — Now let us take another species of Ranunculus, 

 the " bulbous " buttercup. 



Turning to Hooker's flora again, we learn that it is to be recog- 

 nized by some dozen characters which are taken from all parts of the 

 plant ; and although a few points may be common to two species, 

 yet the totality distinguishes each respectively. Hence we can describe 

 a species as being recognized by a collection of constant characters taken 

 from all parts of the plant. If any individuals of a species be found to 

 have something different, though the majority of the characters are 

 the same, it will be a variety, and to discover the cause the observer 

 should at once examine the plant's surroundings, and he will probably 

 be able to account for the aberrant form. 



As an example, a variety of R. bulbosus, naturally a xerophyte, 

 grows in wet, peaty soil.* It has the same flower and fluted flower- 

 stalk, the same leaves, &c, but it is smooth instead of hairy ; it has no 

 " bulb " (strictly a " corm "), it produces offshoots at the base and 

 grows in the lower, wetter sites and avoids the drier parts of the 

 field, where only the common form can grow elsewhere. Moreover, it 

 flowers in August and September instead of June. [This is an un- 

 recorded variety.] 



Miscellaneous Changes. — The usual structure of underground 

 creeping stems is the same, viz. increase of cellular tissue with a 

 decrease of the mechanical, &c. 



If the shoot of a hop, mint, Tropaeolum &c. be buried, when the 

 tip again emerges, the part which has been formed under ground has 

 acquired the structure of a rhizome ; such creeping stems are recognized 

 as specific by systematists. 



Annuals change to biennials under cultivation, as the radish, 

 carrot, &c., and the perennial wild beet also becomes a biennial. The 

 changed conditions of life, of course, have caused the responsive power 

 of the plants to develop the roots of cultivation. 



Such are now more or less hereditary, the cause of the swollen 

 root of the turnip radish or of the turnip itself is the result of the 

 obstruction of a stiff soil, f 



* Near to Poole Harbour. 



f See my History of Cultivated Garden Plants (RM.S.), 



