906 RECORD OF CURRENT RESEARCHES RELATING TO 



homologous to pollen mother-cells, and supports his contrary opinion 

 by cogent arguments. He would rather find a homologue to the 

 pollen-grain in the embryo-sac itself. 



As to the homology of the ovule, Strasburger abandons his earlier 

 view that it is a bud ; he would now rather compare it to a sporangium. In 

 the details of the comparison he does not, however, agree with Warming, 

 but considers the funiculus as the homologue of the pedicel of the si)o- 

 rangium, the nucule that of the capsule itself. In this connection he 

 investigates the phenomenon of oolysis in Bumex and Helenium ; and 

 comes to the conclusion that it is not, as generally supposed, a phe- 

 nomenon of reversion. The fact that in these cases leaf-pinnre finally 

 appear in jjlace of the ovules which spring from separated carpellary 

 structures, and buds in place of the terminal ovules, he regards as a 

 substitution of one structure for another, vegetative organs being pro- 

 duced instead of reproductive. Since the two processes compete with 

 one another, a variety of intermediate forms make their appearance, 

 according as one tendency or the other preponderates. If oolysis were 

 really a reversion phenomenon, it might be expected that a structure 

 would sometimes be formed resembling the sporangium of a cryj^togam ; 

 while, on the contrary, the result is always the production of purely 

 vegetative leaflets, or of a bud. The conception of the ovule as the 

 homologue of a sporangium is confirmed by many facts ; such as the 

 position of the ovules, in certain plants, on the median line instead of 

 the edge of the carpel, and their occasionally unquestionable origin 

 from the axis of the flower. 



With respect to the relationship of the ovule to the pollen-sac, the 

 author maintains that in this case there is no homology; malfor- 

 mations never show a single ovule, but always a considerable number, 

 in i^lace of an anther-lobe ; so that this latter may be regarded as 

 homologous to a sorus. 



In the latter portion of his treatise Strasburger enters into a 

 detailed account of the structure and development of the female flower 

 in the Coniferte and Gnetacese ; and he now regards as ovules the 

 structures previously described by him as ovaries. The investigation 

 of the history of development of the ovule leads him to the important 

 conclusion that the mode of formation of the embryo-sac in Gymno- 

 sperms agrees in essential points with that in Augiosperms. As in 

 these, the mother-cells of the embryo-sac arise from the cell-layer im- 

 mediately beneath the ei)idermis, and from the first step in division. 

 Inner cells become the mother-cells of the embryo-sac, while the 

 outer ones may be regarded as " Tapetenzellen " of Warming. The 

 mother-cells, whether formed singly as in AbietinetB, or in numbers as 

 in Taxacea3, are each divided by septa into three cells ; the lowermost 

 of each now becomes the embryo-sac, and sujii^lants the other two. 



The ovule of Gymnosperms, notwithstanding some not unim- 

 portant differences, is unquestionably homologous, in its first stages of 

 development, to that of Angiosperms. The processes that take place 

 in the embryo-sac are also comparable in the two cases. In Angio- 

 sperms the nucleus divides, and its derivatives i)ass into the ends of 

 the embryo-sac, where four nuclei take the i^lace of the original one. 



