ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 663 



case of a hybrid maize. Before impregnation the two polar nuclei, 

 which display no difference the one from the other, both lie in contact 

 with the oosphere, being about double the size of the nucleus, and con- 

 taining but little chromatin. One of the two male nuclei was seen to 

 fuse with the nucleus of the oosphere, the other with the two polar 

 nuclei ; but the process takes place with so great a rapidity that it is 

 extremely difficult to observe. The division of the polar nuclei also 

 takes place with great rapidity ; but one of the synergids persists for a 

 time after impregnation. The author was never able to observe the 

 actual fusion of the two polar nuclei. 



M. Guignard criticises unfavourably Weber's theory that the nucleus 

 of the embryo-sac may, in some cases, divide parthenogenetically in 

 order to form the endosperm. 



Embryology of Nelumbium.* — H. L. Lyon has studied the embryo- 

 logy of this genus of Nymphaeacere, and concludes, from the resem- 

 blance of the development of the embryo to that of Pistia, and other 

 considerations, that the order should be removed from the Dicotyle- 

 dones, and placed among the Monocotyledones, in the series Helobiee. 



The vascular bundles are closed, and are irregularly placed through 

 the stem. 



The embryo-sac is ovoid at its micropylar end, and tapers down to 

 a narrow attenuation which extends deeply into the nucellus ; as the 

 embryo-sac matures, the nucellar tissue directly in contact with it begins 

 to break down. There also appears, in the antipodal region, a club- 

 shaped cellular structure which obliterates the lower portion of the sac. 

 The embryo goes through four stages, — the spherical, the "mono- 

 cotyledonous," the " dicotyledonous," and the mature stage. In the 

 spherical stage the young embryo becomes surrounded by endosperm- 

 nuclei, between which thin cell-walls are very early apparent. There 

 is no evident suspensor. The single cotyledon makes its appearance as 

 a crescent-shaped mound of tissue round the rear of the embryo, its 

 wings extending forward even with the plumule. In the third stage 

 the cotyledon becomes bilobed through the localisation of growth at the 

 foci, each lobe growing rapidly downward outside the endosperm. The 

 lobes of the cotyledon are not separate structures, but have a common 

 tissue at the base of the embryo. The structure of the ripe seed con- 

 forms more closely to the monocotyledonous than to the dicotyledonous 

 type. 



Embryo-sac of Delphinium.']" — In Delphinium exaltatum, Louise B 

 Dunn finds in the embryo-sac at maturity the normal seven cells ; the 

 oosphere and the synergids being, however, indistinguishable from one 

 another. There is a well-defined endosperm-nucleus, and, at the chalazal 

 end three very large and apparently active antipodals. These, as far as 

 is known, do not disappear, but persist even in the oldest seeds without 

 any trace of degeneration. 



Embryology of the Caprifoliaceae.J — In Viburnum prunifolium, ac- 

 cording to Nellie P. Hewins, the ovules of two of the locules of the 



* Minnesota Bot. Studies, 1901, pp. 643-55 (3 pis.). 



t Proc. Amer. Ass. Adv. Sci., 49th Meeting, New York, 1900, p. 284 



X Tom. cit., pp. 280-1. 



2 y 2 



