June 1891.] BOTANICAL SOCIETY OF EDINBURGH. 147 



not as yet able to give the order in which these phenomena 

 succeed one another. In one endosperm-nucleus the nucle- 

 olus shows fifteen minute unstained areas * or endonucleoli, 

 all of the same size and arranged as the Leads of a rosary, 

 forming an irregular coil, while in another nucleolus these 

 areas are of slightly unequal size and arranged in a circle ; 

 in still another nucleolus, four kidney-shaped endonucleoli 

 are visible ; but perhaps two of the most conspicuous stages 

 are those in which a large central globular endonucleolus is 

 found surrounded by numerous minute ellipsoidal endo- 

 nucleoli, the large central one either possessing a highly 

 refractive plate-like body or not. It is evident that the 

 nucleolus and not the nucleus is the essential element of the 

 cell during the act of fertilisation ; this view, first stated 

 before this Society t and then strengthened by the methods 

 of staining the nucleolus differentially ,| is proved to be 

 correct by the facts discovered during the conjugation of the 

 sexual cells within the embryo-sac.§ That also during cell- 

 division the nucleolus is the main factor, was first pointed 

 out by Dr Macfarlane. || 



If we have, then, spores of different sex within the em- 

 bryo-sac, or spores which, if they germinated, would give rise 

 to male and female prothalli, we would have to ask ourselves. 

 Do we know of any sporangium amongst cryptogams giving 

 rise to such spores ? We find sporangia in the Uquisetinece 

 giving rise to spores of this kind, and not only so, but also 

 means to procure a dissemination ensuring fertilisation, and 

 further, fossil heterosporous Equisetacece are known. As the 

 histological structure of Equisetinece approaches that of Angio- 

 sperms most, may we not reasonably look at the Eqicisefinece 

 as the ancestors of Angiosperms ? 



I shall shortly sum up my view of the embryo-sac by 

 stating that I believe it to correspond to two sporocytes ; one 



* These areas were first observed by Lacaze-Dutliiers, and are called by 

 rieinming, iu Archive fiir microscopische Anatomie, x. p. 259, 1874, the 

 "granule of Schrijn," or "uucleololus," and interpreted by him, as Hesslinghad 

 done before, as "vacuoles ;" Rudolph Arndt uses the term "nucleolulus," first 

 proposed by Mauther ; Macfarlane introduced the term " nucleolo-nncleus " 

 (Trans. Bot. Soc. Edin., 1881, pp. 195, 216), and ultimately substituted, at 

 Professor Rutherford's suggestion, the term " eudonucleolus." 



+ Trans. Bot. Soc. Edin., vol. xviii. (1890), p. 426. 



:|: Ibid., vol. xix. (1891), January, p. 46. 



§ Ibid., vol. xix. (1891), April, p. 89. 



il Ibid., vol. xiv. (1880-81), p. 192. 



