144 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



THE MUTATION THEORY: A OEITICISM/^ 

 By Rev. Professor Geo. Henslow, M.A., F.L.S., V.M.H. 



To explain how Professor de Vries came to broach this theory it is 

 necessary to state his original data and the conditions of his experi- 

 ments. A potato field of nearly 6,000 square yards at Hilversum, in 

 Northern Holland, was abandoned in 1870, and has since lain fallow. 



Oenoihera Lamarchiana was grown in a small bed in an adjoining 

 park, whence it began to spread into the field in 1875. In -abO'wt ten 

 years it extended over the whole of it. In 1889 intersecting paths were 

 made, with the view of planting the plot with trees. The ground, which 

 consists of almost pure sand, was dug up to a depth of three or 

 four feet on both sides of the paths. 



Two " species," as Professor de Vries calls them, had spontaneously 

 appeared — 0. hrevistylis and 0. laevifolia— -first observed in 1887. 



The first experiments were made in 1886, rosettes and seeds of 

 0. Lmuarchana and seeds of 0. hrevistylis being planted in the 

 experimental ground in Amsterdam. 



0. hrevistylis. — It was difficult to distinguish this from 0. La^narck- 

 iana before flowering, except by the rounded apex of the leaves. The 

 flower-buds were shorter, thicker, and blunter, and it blossoms later 

 into the autumn, having a corolla as large as that of 0. Lamar ckiana, 

 but marescent. The pollen was plentiful, and transferred by humble 

 bees; but the style is very sJiort, and the stigmas flatter, the fruits 

 tvere small and /tad only one or two seeds. May not this degeneration 

 in the pistil have been a result of impoverishment from the sandy soil ? 

 Male catkins arise on the weaker twigs, but female on the stronger 

 ones of the Cupuliferae. It was not cultivated. 



An unrecorded number of seeds of 0. laevifolia were sown in a 

 prepared border, and gave rise to both 0. laevifolia and 0. Lamar cliiana ; 

 but, as self-pollination was not practised until 1894, they did not always 

 come true until that period. 



The following are the peculiarities of 0. laevifolia. It was weaker 

 and smaller than 0. Lamar cliiana ', the leaves were flatter; the petals 

 were smaller, narrower, and not emarginate. These features obviously 

 imply a certain amount of degeneration. 



We now come to the Lamarchiana family, commenced in 1895. 

 Since that time Professor de Vries says he manured his ylants heavily, 

 isolating any mutating individual as soon as it could be recognized as 

 such.f In these words, as it seems to me, we have the clue to the 

 explanation of his mutations ; ^or in his * * Species and Varieties : their 



^The Mutation Theory: Experirnents and Observations on the Origin of 

 Species iri the Vegetable Kingdom. By Hugo de Vries, Professor of Botany 

 ab Amsterdam. Translated by Professor J. B. Farmer and A. D. Darbishire. 

 Vol. i. "The Origin of Species by ]\[utation." (Kegan Paul, Trench : London, 

 1910.) 



t p. 222. 



