300 SUMMARY OF CURRENT RESEARCHES RELATING TO 



may always be found another smaller vacuole, and these vacuoles con- 

 stitute the receptive spot of the oosphere. 



The contents of the pollen-tube which enter the oosphere consist 

 of the vegetative nucleus with some cytoplasm and starch-grains, the 

 stalk-nucleus surrounded by its own scanty vacuolated cytoplasm, and 

 the two unequal sperm-nuclei. The larger sperm-nucleus slips from the 

 cell and conjugates with the oosphere nucleus ; the smaller one becomes 

 gradually absorbed. The functional sperm-nucleus and the oospkere- 

 nucleus retain their distinct membranes for a long time after coming 

 into contact ; the chromatin of each nucleus collects in the form of a 

 thick knotted thread near the centre of the separating partition, and the 

 two masses remain distinct until the spirein- bauds begin to segment. 

 The separating membranes disappear just before the spirems are formed, 

 and the nuclear cavities become united. The spindle then arises in a 

 multipolar fashion, twelve chromosomes being supplied from the chroma- 

 tin of the sperm, and twelve from that of the oosphere. A second 

 division soon succeeds tho first, and the four resulting free nuclei 

 rapidly attain full size, and move to the base of the archegone, where the 

 young embryo becomes established. 



Embryo-sac and Embryo of Tulipa.* — A. Ernst has followed out 

 the development of the embryo-sac and ovary in Tulipa Gesneriana. 

 The first division of the nucleus of the embryo-sac takes place immedi- 

 ately before the opening of the flower, and, as in other Liliaceae, a 

 reduction then takes place of the number of chromosomes from twenty- 

 four to twelve, the number in the ordinary vegetative cells being twenty- 

 four. The phenomena attending the development of the embryo-sac do 

 not differ in important points from those in other Liliacese. There are, 

 however, frequently, at the time of impregnation, ovules in which the 

 divisions of the embryo-sac nucleus are entirely or partially suppressed. 

 A coalescence also frequently takes place of the vacuoles between the 

 uppermost and the three other nuclei. The antipodals disappear either 

 before or immediately after impregnation, their function of supplying 

 food-material to the embryo being taken up by a string of cells at the 

 antipodal end of the embryo-sac. 



An interval of as much as 8-10 days intervenes between pollination 

 and impregnation. The double impregnation of the oosphere and of the 

 embryo-sac nucleus was observed in this species as in other Liliacese, 

 and in the genus Tulipa itself by Guignard. f The phenomenon of 

 polyembryony is not unfrequent, in consequence of the rudiment of the 

 embryo dividing into a number of rudiments by transverse walls. A 

 similar phenomenon occurs in some Cupressineaa and Abietinepe and in 

 Erythroiuum.\ 



Crossing of Varieties. § — K. Saj6 discusses the results of a crossing of 

 varieties, chiefly in the cases of the vine and the apple. It is not the 

 seeds only, bat the pericarp, &c. (including the flesh of the apple) that is 

 affected by such crossing. It would appear that the pollen of the grape- 

 vine never travels a greater distance than 6-7 m. In apple and pear 



♦ Flora, Ixxxviii. (1901) pp. 37-62 (5 pis.). * 



t Cf. this Journal, 1900, p. 481. J Of. this Journal, 1896, p. 207. 



§ Promethtsus, xi. pp. 209-12, 225-31, 241-51 (9 figs.). See Bot. Centralbl., 

 lxxxv. (1901) p. 211. 



