ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 589 



BOTANY. 



GENERAL, 



Including- the Anatomy and Physiology of Seed Plants. 



Cytology, 

 Including Cell-contents. 



Chromosomes and Heredity.* — E. M. East publishes a paper deal- 

 ing with the chromosome view of heredity and its relation to the practical 

 problems of plant- breeding. After discussing the evidence favouring 

 the physiological and morphological individuality of the chromosomes 

 and the Mendelian theory of inheritance, the author proceeds to examine 

 the results of work bearing upon (1) the relation of chromosomes to 

 somatic characters ; (2) the relation between the normal behaviour of 

 chromosomes and the transmission of character ; (3) the relation be- 

 tween the peculiar behaviour of the chromosomes and the transmission 

 of character. It is shown that while the behaviour of certain plants 

 and animals favours the view that internal somatic characters, e.g. size 

 of cell, vary directly with the number of chromosomes, the characters of 

 others are quite contrary to it. The evidence bearing upon external 

 characters is equally contradictory ; although apogamy is usually accom- 

 panied by doubling of the number of chromosomes, the phenomenon itself 

 is due to some more obscure cause ; there is no proof that the charac- 

 teristic external features of either species or genera have any direct con- 

 nexion with the number of chromosomes. It appears probable that the 

 chromosomes of the higher animals and plants are of greater complexity, 

 although less numerous, than in lower forms, so that alteration in de- 

 terminants may occur in proportion to the mass of chromatin, without 

 visible variability in the same ratio. The maximum difficulty in the 

 improvement of animals and plants by hybridization is usually directly 

 dependent upon the number of chromosomes, and this difficulty is in- 

 creased by the greater complexity of the chromosomes. The author's 

 experiments show that the chromosomes of tobacco are more complex 

 than those of wheat, and those of the latter are more complex than those 

 of peas and beans. Practical breeding experiments confirm this ratio in 

 the difficulty of improvement of the four genera. Finally, the author 

 shows that anomalous behaviour in heredity is associated with peculiar 

 chromosome mechanism. 



Structure and Development. 

 "Vegetative. 



Ray-pits of Conifers. f — F. U. IT. Brown has examined the medullary 

 rays of Picea and Larix in order to discover if there is variation in struc- 



* Amer. Nat., xlix. (1915) pp. 457-94 (5 figs.). 

 t Ohio Nat., xv. (1915) pp. 542-50 (G figs.). 



