ZOOLOGY AND BOTANY, MICROSCOPY, ETC 57 



•embryos may result from the impregnation of a gamete by a simple 

 fragment of the cytoplasm of a second gamete. 



Double Impregnation in Angiosperms. * — Prof. E. Strasburger 

 carefully reviews all the recent investigations on this process, and comes 

 to a conclusion adverse to Nawaschin's viewf that the formation of 

 endosperm is the result of the fusion of the two polar nuclei, and that 

 where this fusion does not take place, no endosperm is formed. Stras- 

 burger points out that as long ago as 1877 he had established the 

 existence of this fusion in some of our native Orchideaj. The absence 

 of endosperm in the Orchideae is not due to any failure in the fusion 

 of the embryo-sac nuclei, but to the fact that it is not needed for the 

 nutriment of the embryo. The author proposes for the two processes 

 the terms generative impregnation and vegetative impregnation. The 

 object of the former process is the transmission of hereditary properties 

 to the descendants. This is not the function of any process of vegetative 

 impregnation such as the fusion of the polar nuclei with one another, or 

 of one of the generative nuclei with them. An active motion of the 

 generative nucleus within the embryo-sac does not rest on sufficient 

 evidence. Where the pollen-tube nuclei have unquestionably a power 

 of independent motion, they are furnished with cilia, as in the Cycadeae. 



Double Impregnation in Caltha.J — Miss Ethel N. Thomas has con- 

 tinued her observations on the double impregnation in Caltlia palustris. 

 The polar nuclei have generally completely fused before the entrance of 

 the pollen-tube into the embryo-sac. The antipodals are large pear- 

 shaped cells, and, at this period very often contain two nuclei apiece. 

 When the generative nuclei escape from the pollen-tube they are very 

 minute, and may be oblong or dumbbell-shaped, or may have the form 

 of a somew r hat straight S. By the time that the vermiform generative 

 nucleus has reached the middle of the sac, it has enlarged to a very 

 considerable size ; while the nucleus which impregnates the oosphere 

 increases but very little in size. The polar impregnation appears always 

 to take place at a period more or less in advance of that of the 

 oosphere. 



Archegones and Pollen-tubes of Sequoia. § — W. Arnoldi has fol- 

 lowed out his investigation of the endosperm of Sequoia sempervirem by 

 some observations on the corpuscles (archegones) and pollen-tubes. 



The archegones are formed laterally in the endosperm, and are either 

 single or associated in groups. Each archegone arises from a single 

 peripheral endosperm-cell. Their structure resembles that of the 

 Oupressineae, but they have a bicellular neck, and, like the Cupres- 

 sineae, are destitute of a ventral canal-cell. A complete covering 

 layer is never formed round the archegones, whether they are single 

 or collected into groups ; single endosperm-cells assume the character 

 of covering cells. The position of the pollen-tubes corresponds to that 

 of the archegones ; they force their way in between the nucellus and the 

 endosperm. Their structure corresponds to that in the Cupressineae. 



» Bot. Ztg., lviii. (1900) 2" Abt., pp. 293-316. Cf. this Journal, 1000, p. 6S9. 

 t Cf. this Journal, 1900, p. G02. 



X Ann. of Bot., xiv. (1900) pp. 527-35 (1 pi.). Cf. this Journal, 1900, p. 605. 

 § Bull. Soc. Imp. Nat. Moscou, 1899 (1900) pp. 405-22 (2 pie. and 4 figa.). 

 (German). Cf. this Journal, 1900, p. 482. 



