Varietäten, Descendenz, Hybriden. 235 



(C) nachg-ewiesen. Ausserdem geht aus den Untersuchungen hervor, 

 dass Unabhängigkeit von Merkmalen nicht immer mit Unabhängig- 

 keit der Faktoren für diese Merkmale Hand in Hand geht. Hieraus 

 ergibt sich sehr deutlich wie umsichtig man bei der Beurteilung 

 der Resultate einer einzigen Kreuzung zu verfahren hat. Moll. 



'& 



Willis, J. C, The Evolution of Species, with reference 

 to the Dying Out of Species. (Ann. Bot. XXX. p. 1—23. 2 

 text-figs. 1916.) 



This paper forms a continuation of the series of memoirs, 

 based largely on a study of the flora of Ceylon, in which the 

 author has elaborated certain new views upon the significance of 

 the facts of distribution, and, in particular, upon the inability of 

 Natural Selection to account for these facts. The present contribu- 

 tion is the result of an analysis of the Ceylon flora, in which the 

 facts and figures are taken from Trimen's Flora of Ceylon, and 

 are thus not to be explained away as having been coUected with 

 any bias towards one theory rather than another. Trimen divides 

 all species into six classes, „Very Common, Common, Rather Com- 

 mon, Rather Rare, Rare, Very Rare", these expressions represen- 

 ting chiefly the area occupied, as marked out by the most outlying 

 stations. The author has drawn up tables showing the number of 

 species coming under each head in the case of 1) endemic Ceylon 

 ssp., 2) Ceylon— Peninsular— Indian spp., and 3) those spp. which 

 are of wider distribution. In order to get a numerical expression 

 for the degree of rarity of the different groups of species, he u.ses 

 the numbers 1 to 6 for Trimen's six classes from Very Common 

 to Very Rare. He then multiplies the total under each of the heads 

 (Very Common. Common, &c) by the mark 1, 2, &c) corresponding 

 to that head, which gives as it were the actual number of „units 

 of rarity" present altogether. The average rarity is then calculated 

 by dividing the number of units of rarity thus obtained by the total 

 number of species. Worked out by this method the average rarity of 

 the Ceylon endemics proves to be 4.3, the Ceylon — Peninsular — In- 

 dian spp. 3.5, and the species of wider distribution 3.0. In other 

 words the widely distributed species are by far the commonest, and 

 much commoner than the mean of the whole flora. which is 

 obviously 3.5, the mean between 1 an 6, while the endemic species 

 are much rarer than this mean. Not only do the grand totais 

 show these figures of rarity for the three groups into which the 

 author divides the Ceylon flora, but the figures for each family 

 taken separately approximate remarkably to the same numbers. 



The interpretation which the author puts upon these facts is as 

 follows. As all the plants and all the families behave alike, it is 

 evident that their grouping and distribution must be the result ofa 

 cause which acts upon all with practically even pressure. Now 

 Natural Selection could not do this, for in its essentials it is of a 

 differentiating nature. The only cause, in the author's opinion, 

 which thus acts evenl}^ upon all is age, and he is inclined to think 

 that the area occupied by any given species at an}'- given tirae in 

 any given countr}^, is to a large extent an indication of the age of 

 that species in the country (not its absolute age). The widely 

 distributed species, which must on the whole be the oidest, are the 

 commonest; the Cej'-lon- Indian next oidest and next commonest, 

 and the endemics, which are the youngest, and which are to be 



