24 8 • Varietäten, Descenderiz, Hybriden. 



as to which more nearly represents the truth. But one may at 

 least advance the view, to which the whole of this paper has been 

 leading, and which one may hope will be heartily concurred in 

 by both sides in the selection controversy, that the great outstan- 

 ding need in research on the problem of evolution in general, 

 and of selection in particular, is more, and more searching, inves- 

 tigations as to the causes of genetic (factorial) Variation. That 

 both sides realize this need, and are all the time bending more 

 and more energies to its selection, is indeed of great value for 

 the future of that branch of biological science. 



M. J. Sirks (Wageningen). 



Longley, W. H., The selection problem. (American Naturalist 

 LI. p. 250—256. 1917.) 



The paper is a reply to Pearl's above reviewed article, and 

 gives this conclusion: 



It appears that neither genetic research nor studies upon 

 elimination closely limit the possibility that selection has played 

 a very important part in evolution. In addition recent field-studies 

 demonstrate novel facts of common occurrence which must appa- 

 rently be ascribed to the action of this factor. Hence as was sugge- 

 sted in the beginning of his paper, the author thinks Pearl would 

 seem to overemphasize the importance of Variation, and to attach 

 too little significance to selective agencies in determining the 

 course of racial history. M. J. Sirks (Wageningen). 



Willis, J, C, The Endemie Flora of Ceylon, with Refe- 

 rence to Geographical Distribution and Evolution in 

 general. (Phil. Trans. Roy. Soc. Lond. Ser. B. CCVI. p. 307— 342, 

 25 Tables. 4 Textfigs. 1915.) 



Ceylon contains 149 families, 1027 genera and 2809 species of 

 flowering plants; 91 families and 324 genera (of which 23 are 

 endemic) contain 809 endemic species. Six families with 7 species 

 have all species endemic; 4 families with 91 species out of 102 have 

 over 75 per cent, and 14 with 255 out of 435 have over 50 per cent 

 of their number endemic. Trimen divides these according to rarity 

 into six classes: Very Common, Common, Rather Common, Rather 

 Rare, Rare, Very Rare. Marking these from l to 6 the mean rarity 

 is 3.5. Dividing the fiora into three groups: Ceylon (809 sp.), 

 Ceylon-Peninsular India (492) and of wider distribution (1508), 

 the endemics are found to increase in number from 19 VC to 

 233 VR, and have rarity 4.3, while the "wides" go in the other 

 direction, with rarity 3. Thus the rarest plants in Ceylon are the 

 local endemics, the next most rare are those also common to Penin- 

 sular India, and the commoncst those of wider distribution. It is 

 concluded that the local endemic species have not been developed 

 in any kind of advantageous response to local conditions. They are 

 much rarer than those species which are also common to Pen in- 

 sular India and these again than those of wider distribution. There 

 has been ample time for these endemics to become VC or really 

 adapted to local conditions, yet only 19 out of 809 have done so. 



The second conclusion drawn is that, on the average, the 

 commonness of a species depends upon its age from the time of 

 its arrival in, or evolution in, the country. In other words, on the 



