498 SUMMAEY OF CUREEJ^T RESEARCHES RELATING TO 



BOTANY. 



GENERAL, 



Including the Anatomy and Physiology of Seed Plants. 



Cytology, 

 Including- Cell-contents. 



Tetraploid Mutants and Chromosomes.'*' — R. R. Gates is continu- 

 ing bis work upon CEnothera, and now publishes a paper dealing witb 

 giantism and tetraploidy. Although thirty cases are known of plants 

 having tetraploid, or a higher number of chromosomes, no instances 

 have been found in wild plants. The occurrence of triploid mutants is 

 due to the union of a diploid with a haploid germ-cell, and the tetraploid 

 mutant 0. gigas is probably the result of apogamous development of an 

 unreduced megaspore-mother-cell, i.e. a suspended mitosis just before 

 or just after egg-formation. It appears that mutation changes occur 

 not only in meiotic divisions, but also in aposporous development of the 

 gametophyte, in bud mutations, and in early division of the Qgg. The 

 pollen-grains of the offspring of giant forms differ very strikingly, and 

 the percentage of quadrangular and triangular grains is a useful pre- 

 liminary criterion as to the number of chromosomes. Certain characters 

 of 0. gigas^ e.g. the strong biennial habit, larger seeds, short fruits and 

 susceptibility to frost, are the direct result of the tetraploid condition. 

 Fourteen different types of chromosome-change have been observed in 

 CEnothera. The variations of 0. gigas are doubtless due in part to loss 

 of chromosomes and partly to the fact that it is a progressive mutant. 

 Although some of the characters are Mendelian in their behaviour after 

 they have arisen, Mendelian combinations are inadequate to account for 

 their first appearance. Finally the author agrees with Nilsson in think- 

 ing that many mutant differences are due to changes which are funda- 

 mentally quantitative. 



Pollen-grains of Hemerocallis.t — P. N. Schlirhoff has continued 

 the investigations of Strasburger and others upon the pollen-grains of 

 Hemerorallis fulva, and finds that we have here a typical case of karyo- 

 mere-formation, a point of especial interest, since such formations are 

 only known in two other plants, viz. Trillium and Chara. The pollen- 

 grain ripens extremely early, and nuclear division occurs at the time 

 when the exine appears as a heart-shaped mass on one side of the 

 pollen -grain. 



The tendency of the pollen-grain to enlarge, sets up centrifugal 

 forces, which separate the chromosomes from the nuclear spindle and 



* Biol. Centralbl., xxxiii. (1913) pp. 92-150 (7 figs.). 

 t Jahrb. wiss. Bot.. lii. (1913) pp. 405-9 (1 pi.). 



