10 Descendenz und Hybriden. 



and States that in specimens of Lychnis, from various localities, 

 examined by him the number of hairs per square centimetre 

 varied enormously, in 112 plants of one race from Shotover 

 Hill he found a ränge from one individual entirely glabrous to 

 one with 1106 hairs per Square centimetre the meaning of the 

 term „hairy" thus becomes very vague. 



The experiments of Miss Saunders and Mr. Bäte so n on 

 Lychnis and Datiira are discussed with reference to the diffi- 

 culties caused by using Mendel 's categories as Statistical 

 Units. 



It is noted that when these authors state that Mendei's 

 Laws are ciosely obeyed in the phenomena resulting on crossing 

 Lychnis vespertlna and Lychnis diiirna with white and red 

 glabrous varieties, the deviations from that Law observed in 

 the earlier history of the glabrous variety previously used by 

 de Vries, appear to have escaped them, yet from de Vries 

 they apparently received their stock. The paper concludes 

 with the remark that the confusion introduced into the second of 

 their experiments on the spinyfruited, and smooth-fruited races of 

 Datnra by the use of Mendelian categories is even greater than 

 in the case of Lychnis. Karl Pearson. 



Weldon, W. f. R., Professor de Vries on the Origin 

 of Species. (Biometrika. Vol. I. Part HI. 1902. p. 365 

 —375.) 



This is a review of Professor de Vries' „Mutations- 

 theorie". The evidence of de Vries concerning the instabi- 

 lity of forms produced by long continued selection is examined 

 and is considered to be inconclusive, special attention is called 

 to the neglect of the influence of external conditions, and the 

 author describes experiments of his own on hens' eggs in 

 which he found the ammon was suppressed by change of 

 external conditions. It is pointed out that the views of 

 de Vries cannot be maintained unless it can be proved that 

 Francis Galton and Karl Pearson are wrong in their 

 conclusion that the focus of regression of each generation is 

 its own mean, and that de Vries has misinterpreted the 

 theory in not allowing for the diminution of regression with 

 repeated selection. 



The experiments of de Vries on Maize are discussed, and 

 it is shewn that they give proof that regression to the original 

 race mean does not occu.r, thus furnishing proof that the 

 Statement on which the whole theory of the instability of 

 varieties depends, is erroneous. The author also considers that 

 the Statements as to the character of regression among the 

 offspring of mutations are unsupported by satisfactory proof. 



The experiments on clover are discussed and it is pointed 

 out that the only difficulty in reconciling the results of these 

 experiments with Darwin 's Theory of Natura! Selection arises 



