552 SCIENCE PROGRESS 



which have the greatest number of widespread species, and 

 which were therefore presumably colonised at a relatively early 

 date. Such facts, and the limited average range of endemics 

 as compared with non-endemics, point clearly to the influence 

 of the time factor. That is, the endemic species is, in most 

 cases, one which has not had time to spread, or alternatively has 

 been hindered from so doing by geographical or biological 

 barriers. 



All the 1582 endemic genera of the world's islands are con- 

 sidered in this paper, and it is shown that the first forty families, 

 in order of the number of endemic island genera which they 

 embrace, include no fewer than thirty-one of the first forty 

 largest families in the world. Herbaceous families tend to 

 present few endemics, which is consistent with the probably 

 more recent origin of the herbaceous type. 



Of the 145 non-endemic families which have endemic genera 

 on islands, 90 per cent, reach both the Old and New Worlds, 

 while only 52 per cent, do so in those families which contain no 

 endemic genera. 



The facts, then, appear to indicate that the endemics of 

 tropical islands are almost entirely the more recently produced 

 species, and probably but rarely unsuccessful survivals. 



Norman Taylor, in the same journal, discusses the endemic 

 flora of the Bahamas. This consists of 185 species, embracing 

 132 flowering plants out of a total of 894 species. Analysis 

 shows that the percentages of the species found on one, two, 

 three, or many islands do not differ appreciably as between the 

 endemics and non endemics, and it is suggested that the age 

 of these Bahama endemics cannot be measured either by their 

 area or frequency. It is, further, in contrast to Willis's results 

 that the percentage of herbaceous species is here greater for 

 the non-endemics (59.3 per cent.) than for the endemics (39.3 

 per cent.). The facts appear to suggest that the numerous 

 endemics are related to the peculiar climatic conditions rather 

 than to age. 



Genetics, etc. — Ostenfeld has shown that in the section Pilosella 

 of the genus Hieracium, new forms have arisen in consequence 

 of hybridisation, and are then kept pure by apogamy. In the 

 section Archieracium very few species are sexual, amongst the 

 exceptions being H. unibellatum and H. virga-aurea. Recently, 

 Ostenfeld has described {Genetics, September) the origin of two 

 apogamic mutants from a parent which was itself apogamous, 

 viz. Hieracium rigidum. It is suggested that in both sub-genera 

 the real cause of the appearance of new forms is hybridisation 

 in the past, whilst apogamy is responsible for their constancy. 



Lloyd Williams, in a preliminary account {Ann. Bot., 

 October), describes the gametophytes of Laminaria and Chorda. 



