VarieüUen, Descendenz, Hybriden. 631 



"modifiers". Also palaeontological records afford further evidence 

 of the gradual evolution of characters that are disconünuous in 

 inheritance, as Osborn's studies have shown. 



M. J. Sirks (Haarlem). 



Cook, O. F., Date palm allies in America. (Journ. of Here- 

 dity. VI. p. 117-122. 1915.) 



The very wide distribution of the species of Phoenix in the 

 Eastern Hemisphere makes it difficult to credit a complete ex- 

 tinction of the group in the Western Hemisphere. Date palms 

 are known from all of the tropical and subtropical regions of the 

 Old World, from India through Africa to the Canary Islands, 

 though they do not extend far into the Chinese region, to Au- 

 stralia, or to the islands of the Pacific. This is in contrast with 

 the distribution of the Asiatic fan-palms, which are well represented 

 in eastern Asia and the Pacific islands. The two genera 

 Phoenix and Inodes enjoy to a greater extent than most of their 

 relatives the same adaptive advantage, that the seeds retain their 

 vitality for long periods in the dry State. Phoenix is most closely 

 related with Chamaerops and Trachycarpus. 



A number of palms, that seem in one or another sense allied 

 with the date palm are found in America, but none of these 

 Shows a near relationship. F. i. the seeds of Brahea dulcis are very 

 much alike those of a date, including the groove along one side, 

 but otherwise not. Most closely resembling seems to be the Mexican 

 Palmetto, Inodes exul. 



If the fossil seeds from Texas described by Berry, represent 

 a true date palm, it may be expected that remains of other Asiatic 

 genera of fan-palms will be found in America. On the other band, 

 if the fossils represent a collateral relative of the date palm the 

 Separation between Phoenix and the Old World fan-palms may 

 have occurred in the Eastern Hemisphere. In view of the 

 analog)'^ presented by Brahea, the former presence of Phoenix in 

 America can hardly be determined from the seeds alone, 



M. J. Sirks (Haarlem). 



Cook, O. F., Two classes of hybrid s. (Journ. of Heredity. VI. 

 p. 55-56. 1915.) 



The use of distinct names for the two principal classes ot hy- 

 brids would be in the interest of convenience and intelligibility. 

 The ordinal designations "first generation hybrids", ''second gene- 

 ration hybrids", "third generation hybrids" etc., are cumbersome 

 and confusing in actual use. The Mendelian Symbols "F^", "F2", "F3" 

 etc. serve for technical or esoteric writing, but are awkward 

 typographically and have little meaning for the general reader. 

 Borh of these Systems of designation are essentially misleading to 

 the Student in that they leave out of account the wide biological 

 differences between the so-called first or Fj-generation of hybrids 

 and the second and later generations. 



As the so-called first generation of a hybrid is developed while 

 the conjugation begun by the parental germ cells is still in progress, 

 it can be described as the conjugate generation. The so-called 

 second or Fg-generation is really the first generation that can be 

 considered as a complete product of the conjugation that was begun 

 by the original germ-cells. The name perjugate seems appropriate 



