ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. 621 



and four below. Eound three of the upper nuclei are formed cells, 

 the synergidee and the ovum ; sometimes antipodals are produced 

 below, but generally the nuclei appear to remain free. During this 

 time the lower daughter-cell retains nearly the same size ; later it 

 usually has four nuclei ; in a few cases it was seen to be divided by a 

 delicate vertical septum ; in adult ovules it is always readily visible ; 

 the septum which separates it from the embryo-sac has thickened 

 considerably. 



In Tulipa Gesneriana a large sub-epidermal cell of the nucellus 

 itself becomes the embryo-sac, without first undergoing any division. 

 At a certain stage a vacuole is formed, and in normal cases only one 

 of the nuclei remains in the upper part of the embryo-sac, the three 

 others occupying the lower part. Subsequently all the nuclei divide, 

 two being then formed above and two groups of three below. The two 

 upper ones then again divide, forming the two synergidfe and the 

 ovum, the fourth remaining inactive. The two groups of three nuclei 

 at the base of the embryo-sac vary in their behaviour. The three 

 upper ones often unite, forming a crescent-shaped band ; in other 

 cases the fusion is incomplete ; sometimes the nuclei of this group 

 divide again. In the mature embryo-sac all the nuclei of this group 

 are generally fused into one large one, which may subsequently unite 

 with the fourth upper nucleus. The three nuclei of the lower group 

 also sometimes unite ; very rarely are antij)oclals formed round them ; 

 more often they remain unchanged, and finally disappear. 



In Lilium hulbiferum, as in Tulipa, one large sub-epidermal cell is 

 directly transformed into the embryo-sac. In other respects the 

 development is more simple. After the formation of four nuclei, two 

 move to the upper, two to the lower end of the embryo-sac. After 

 fresh divisions of the nuclei, there are, in the upper part, besides the 

 ovum, two synergidae and one free nucleus ; in the lower part one 

 large free nucleus and three antipodals. Cell-walls are frequently 

 formed round the synergidaa, and the protoplasm often assumes a ray- 

 like disposition round the nuclei, this being specially marked when 

 the nuclei are in process of division. 



Strasburger's 'Cell-formation and Cell-division.'* — The third 

 edition of this work contains the record of fresh observations on 

 several points, and considerably enlarges our knowledge of the internal 

 life of the cell. In particular the author insists more strongly than 

 before that the division of the nucleus and cell-formation are two 

 distinct processes, which may be completely separated from one 

 another, although in many cases they come into contact. It is not the 

 nucleus which forms the centre of attraction in cell-formation ; 

 forces, on the contrary, are at work in the protoplasm which cause 

 division in it as well as in the nucleus. There is no doubt that the 

 nucleus plays a very important part in the life of the cell ; Strasburger 

 attributes to it, though without positive proof, the function of a former 

 of albumen. 



* Strasburger, E., ' Zellbildung u. Zelltheilung,' 3rd ed. 392 pp. (15 pis.). 

 See Bot. Ztg., xxxix. (1881) p. 52. 



Ser. 2.— Vol. I. 2 T 



