194 SUMMARY OF CURRENT RESEARCHES RELATING TO 



the exception of the water and salts they are afterwards elaborated by 

 the parasite. The parasitic habit is accidental and partial, and has been 

 determined by necessary adaptation to the medium in which the plant 

 lives. S. ft. 



Reproductive. ' 



Inheritance of Sug-ar and Starch Characters in Corn. — E. A. 

 Harper {BulL Torr. Bot. GL, 1920, 47, 137-86, 3 pis.). Four genera- 

 tions of plants, obtained by crossing a sweet with dent corn, were 

 studied in order to establish the facts as to the occurrence of inter- 

 mediates between starch and sugar corns and the behaviour of these 

 when grown and self-fertilized. The observations show that the 

 parental germ-plasms are separated in the reduction-division, and that 

 the recombination of the gametes so produced is in accordance with the 

 laws of chance assumed in Mendelian conceptions, Ijut intermediates 

 occur the characters of which are heritable to a considerable degree. 

 Selected intermediates give a higher percentage of intermediates than 

 pure parents. 



The general occurrence of intermediates appears to be due not only 

 to the bringing together of divergent or contrasting pairs of charac- 

 teristics, but to the exigencies of sexual reproduction itself ; variability, 

 however, is more characteristic of the offspring of impure races than of 

 pure races. The very nature of the gametes and of the chromosomes 

 makes it improbable that the germ-plasms remain unaltered during the 

 reproductive processes. Constitutional differences in the gametes are 

 likely to be responsible for wider and so-called sudden variations known 

 as mutations, sports, monstrosities, etc., while the complex nature of 

 the reduction, fusing and pairing processes may be regarded as respon- 

 sible for those fluctuating normal variations which are often confused 

 with the not directly heritable variations due to external environment. 

 External conditions may, however, influence the complex of reproductive 

 processes. 



The characters, sweet and starchy, are typically metidentical 

 characters. The presence of sugars and dextrin gums leads to shrinkage 

 of the cell, and the whole kernel becomes wrinkled, while the presence 

 of more solid starch-grains prevents this shrivelling and the kernels 

 remain plump and round. The fixity of type resulting from asexual 

 reproduction is sufficient to furnish a fairly stable product for the 

 market, but is not absolutely stable. Sugar and starch characters are 

 not due, as is often supposed, to a pair of fixed Mendelian characters. 



S. G. 



CRYPTOGAMS. 



Pteridophyta. 



Old Red Sandstone Plants from the Rhynie Chert. Part II. : 

 Additional Notes on Rhynia Gwynne-Vaughani. with Descriptions 

 of Rhynia major and Hornea Lignieri. — Pi. Kidston and AV. H. 

 Lang {Trans. Roy. Soc. Edinburgh, 1920, 52, 603-27, 10 plates). 

 A further account of the remarkably preserved structure of early 



