ZOOLOGY AND BOTANY, MICKOSCOPF, ETC. 251 



application of pigments to be chromatin structures, and which de- 

 velope into the nucleoli of the endosperm-nuclei. The nucleoli 

 contain a very thin finely granular border of protoplasm ; its granules, 

 apparently grouped into short threads, surround the central nucleolus 

 in a radial manner. The layer of protoplasm thus formed becomes 

 gradually detached from the surrounding protoplasm of the embryo- 

 sac, loses its radial framework, and forms at length a clear zone 

 round the nucleolus containing only a few scattered granules. 



The nuclei in the parietal layer are sometimes formed separately, 

 whether in the lower or upper part of the embryo-sac ; sometimes in 

 groups. 



Constitution of Albumin.* — From the reaction of superosmic acid 

 O. Loew argues that the leucin and tyrosin compounds do not occur 

 ready formed in the molecules of albumin ; but that they are readily 

 produced — especially the benzol-nucleus of tyrosin — when albumin 

 undergoes decomposition. The basis of the formation of albumin ho 

 considers to be a process of condensation rather than one of com- 

 plicated synthesis. 



Fertilization of Sarracenia purpurea. f — F. Hildebrand describes 

 the mode of pollination in Sarracenia purpurea, where the male and 

 female organs are mature at the same time, but their relative position 

 is such that fertilization is almost impossible without the assistance 

 of insects, and self-fertilization is even then rendered very difficult. 



He also describes the arrangements for self-fertilization in a water- 

 plant, Heteranihera reni/ormis, and for cross-fertilization in Salvia 

 carducea, which differs from other species of the genus in the 

 immotility of its stamens. 



Sexual Relations in Monoecious and Dioecious Plants.^ — F. 

 Heyer has carried out a number of experiments with the view of 

 determining the causes of the differentiation of sex in unisexual plants. 

 As regards dioecious plants, the result .of experiments with 21,000 

 specimens of Mercurialis annua and 6000 of Cannabis saliva was that 

 external conditions have no influence on the production of seedlings 

 of one or the other sex. The number of seedlings of each sex is very 

 nearly the same ; in the former species the proportion of male to 

 female individuals was about as 105-85 to 100; in the latter, about 

 as 86 to 100. Both species exhibit also secondary sexual differences 

 in the vegetative organs. 



A second series of experiments to determine whether external 

 conditions of temperature and soil caused any difference in the 

 proportion of male and female flowers in monoecious plants (Urtica 

 urens, Atriplex, Spinacia, Xanthium, Cucurbitace^) yielded also only 

 negative results. 



The general conclusion is that the sex of the individual is deter- 

 mined at an earlier period than the ripening of the seed ; whether 

 before or after fertilization cannot at present be said. 



* Pfliiger's Arch. f. d. Ges. Physiol., xxx. (1883) pp. 368-73. 

 + Ber. Deutsch. Bot. Gesell., i. (1883) pp. 455-60 (1 pi.). 

 X Ber. Landwirthsch. Inst. Halle, Heft v. See Bot. Ztg., xli. (1883) p. 873. 



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