58 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Be Vries names seven mutants from Oenothera Lamarckiana. The 

 descriptions are more or less of the same nature as the following : 

 " 0. leptocarpa, flowers late, and has long, slender fruits which seldom 

 ripen. 0. nanella, dwarf, weak, often incompletely developed, small 

 quantity of pollen or none. The stigmas stick together. 0. elliptica, 

 weak and very early overgrown ; pollen often barren. " This feature," 

 he adds, "is quite normal for many species of Oenothera," &c. 



The reader will see that the mutation theory is only a special 

 instance of results of direct response to new conditions of life. In fact, 

 from De Vries' descriptions his mutants seem to come nearer to 

 Darwin's " injurious variations " than " favourable ones " ! For 

 further details I would refer the reader to my notices.* 



Nature of Proofs. — What are the proofs of Darwin's alterna- 

 tive ? Scientific proofs are either by Induction, i.e. the accumulation 

 of numerous, independent cases, all conspiring to establish the same 

 conclusion or probability, until the latter amounts to a " moral 

 conviction." Secondly, Experimental Verification. This is usually 

 regarded as the most important. 



The following few examples may be taken as illustrations from 

 Ecology : — 



Cultivation, f — Edible roots. 



Xerophytes. — The " mimicry " seen between the North American 

 Cactaceae as well as of Agave, with African species of Euphorbia and 

 Aloe respectively, is presumably the result of the same cause, or the 

 " direct action " of drought, with the " response " of making similar 

 forms of the stems or leaves for water-storage. 



The genus Pereskia — a tree with ordinary leaves, but growing by 

 the Amazon river — may be contrasted with Cactus, as both belong to 

 the same family. 



As a spinescent type, Ononis spinosa may be compared with 

 0. inermis ; while the seeds of the former, germinating and growing 

 up in a soil kept moist, result in the latter form without spines. 



Hydrophytes. — The Water Crowfoot, Ranunculus aquaiilis Linn., is 

 an excellent example whereby to prove the Origin of Species by means 

 of the direct action of the conditions of life. Both of our two greatest 

 systematic or descriptive botanists of the last century, Mr. G. Bentham 

 and Sir J. D. Hooker — joint authors of the " Genera Plantarum " 

 — wrote British Floras ; but while the former in his " Handbook 

 of the British Flora " (ist ed.) has only one species, Hooker has 

 described eight in his " Students' Flora of the British Isles." 



Bentham observes, when describing J?, aquaiilis'. "Many of the 



forms appear to depend so much on the situation the plant grows in, 



that we can only consider them as mere varieties." He here unwittingly 



refers to the true cause of all varieties and species of plants in the world, 



exclusive, of course, of crosses and hybrids. 



* The Mutation Theory, Journ. Royal Hort. Soc. xxxi. 1907 and xxxvi. Pt. I. 

 p. 144. 



f For other examples see The Origin and History of Garden Vegetables 

 (R.H.S.). 



