XENIA 113 



we find a notable increase in the present group. Eighteen of the 

 species given in Dr. Braithwaite's tiphagnacece are European. Dr. 

 Warnstorf has increased them to fifty. How many of these are 

 native to our country remains to be ascertained with the help of 

 Mr. Horrell's synopsis. 



Mr. Horrell has thrown himself into his task with ardour, and 

 has performed it conscientiously. He has gone afield and col- 

 lected; he has determined and revised thousands of specimens. He 

 gives us a key to the species, detailed descriptions of the species and 

 varieties, with their geographical distribution, a bibliography, and 

 an index. The discrepancy between the number of species in the 

 key and the number in the body of the book is explained by a note 

 on p. 39. Whilst Mr. Horrell was publishing the instalments of 

 his work in the pages of this Journal last year, he learned that Dr. 

 Warnstorf had revised his conclusions as to the group Cmpidata. 

 Consequently he had to introduce a revised key of this group, and 

 to add the descriptions of eight more species. 



It is to be regretted that a larger edition of separate copies of 

 this useful book was not printed o£f. Of the 100 copies prepared, 

 eighty have already been taken up by the Moss Exchange Club, and 

 less than a score are left in stock. 



A. G. 



Xenia, or the i in mediate effects of Pollen in Maize. By Herbert J. 

 Webber. U. S. Department of Agriculture, Bulletin no. 22. 

 8vo, pp. 44, 4 plates. Washington. 1900. 



This paper deals in a most interesting manner with the phe- 

 nomenon of "Xenia"— a term appHed to the changes that are 

 produced in seed by cross- fertilization. That the hybrid plant 

 should be changed in character was to be expected, but that the 

 seed, apart from the embryo, should be altered was difi&cult to 

 understand, though there could be no doubt that there was very 

 distinct alteration. It is only recently that this mysterious influence, 

 or " Xenia," has been satisfactorily explained by the discovery of a 

 double fecundation. Prof. Nawaschin and Prof. Guignard, working 

 independently of each other, discovered this fact about two years 

 ago, while working on the fertilized embryo-sac of Lilium and 

 Fritillaria. They found that both the nuclei of the pollen-tube 

 passed over into the embryo-sac ; that one fused with the nucleus of 

 the ovum, and the other with the definitive nucleus of the embryo- 

 sac, and that the endosperm to which the latter nucleus gives rise 

 is thus equally with the embryo the product of fertilization, and 

 bears the impress of the male plant. 



There is no plant, Mr. Webber goes on to state, in which the 

 occurrence of Xenia is so well substantiated as in Maize, though 

 double fertilization has not yet been observed in any of the cereals, 

 and his conclusions are necessarily theoretical. The generative 

 nucleus in grasses has, however, been noted and described as of 

 spiral form, thus agreeing in form with the male nucleus in Liliitm 

 Martagon described by Prof. Guignard, and further confirmed by 

 Miss Sargant. 



Journal of Botany.— Vol. 39. [March, 1901.] i 



