ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 807 



placed at the same level ; more often they are superposed ; sometimes 

 they multiply, ami form a tissue of a special nature. The fusion of 

 the polar nuclei takes place towards the centre of the sac, or higher 

 up, near the oosphere. 



The author then traces the genetic history of the embryo-sac of 

 angiosperms through the various classes of the higher cryptogams, and 

 finally through the gymnosperms. The pollen-grain of gymnosperms, 

 in which Strasburger has demonstrated the existence of a single 

 partition, presents a close analogy to the microspore of Selaginella. 

 One of the two cells developes into the pollen-tube, and represents an 

 antheridium ; the other is equivalent to a rudimentary male prothal- 

 lium. The naked cells, observed by Hofmeister and Strasburger at 

 the extremity of the pollen-tube, may be compared to the mother-cells 

 of antherozoids, and complete the analogy, which is rendered more 

 evident by comparing the mode of formation of the microspores of 

 vascular cryptogams with that of the pollen-grains of gymnosperms. 

 The researches of Strasburger and Elfving have shown the existence 

 uf a similar division-wall in the pollen-grain of angiosperms. Two 

 cells are thus formed ; one of these, the vegetative cell, further divides 

 into a prothallium of two or three cells ; the other, the nucleus of 

 which has not been observed to divide, except in the Cycadeas, becomes 

 the pollen-tube ; the nucleus, situated at the extremity of the tube, 

 appears to play an important part in the process of fecundation. 



As regards the homology of the female organs, the author contends 

 that the facts support Strasburger's theory that the embryo-sac is the 

 homologue of the macrospore of the higher cryptogams, and not the 

 nucellus, as Warming maintains, a view which is inconsistent with 

 the remarkable phenomenon of the fusion of the polar nuclei. The 

 female prothallium is represented in gymnosperms by the endosperm, 

 in angiosperms by the antipodals and the two polar nuclei ; the 

 synergidfe are endosperm-cells endowed with a special function ; and 

 the endosperm of angiosperms, which is formed only after fecundation, 

 by division of the secondary nucleus of the embryo-sac, is the result 

 of the resumption of an interrupted development. 



Development of the Embryo in Lupinus.* — An apparent anomaly 

 in the embryogeny of certain species of Lupinus is explained by L. 

 Guignard as clue to differences in the structure of the ovule. The 

 species of the genus may be divided into two groups, according to the 

 number of ovular integuments ; one group, represented by L. poly- 

 phjllus, having only one integument; the other, represented by 

 L. luteus, having two ; and this is correlated with a difference in the 

 structure and development of the suspensor or proembryo. The 

 number of pairs of cells of which the suspensor is composed, and con- 

 sequently the length of this organ, varies with the species ; but in all 

 those which have only one integument, it finally becomes disinte- 

 grated, and the cells which constituted it arrange themselves on 

 the median line from the micropyle to the embryo, which is always 



* Bull. Soc. Bot. France, xviii. (1SS1) pp. 231-5. See this Journal, ante, 

 p. 644. 



