280 NOTICES OF BOOKS AND MPiMOIRS. 



which latter immediately itself undergoes division. The large 

 cell, which is the yoimg emhryo sac, expands and presses against 

 the two crowning cells, and while doing so its nucleus divides. The 

 new nuclei immediately separate, one going to the toj) and the other 

 to the bottom of the sac, each accompanied, in its progress, by 

 plasma, and sej)arated at first by an incompletely-formed cell- 

 plate, the disappearance of which is followed by the formation of 

 a large vacuole in the centre of the sac. By this time the two 

 crowning cells have become so compressed that they are visible no 

 more than as a cap. The innermost sac-neighbouring row of 

 nuclear cells now shows signs of disorganisation, after which the 

 two nuclei of the sac divide ; but the cell-plate not being completed, 

 there are now two free nuclei at each pole, round which almost the 

 whole of the plasma is collected. These j)airs of nuclei next 

 divide each in a j)]ane more or less inclined to that in which its 

 fellows division occurs ; this time, however, a complete wall 

 separates the sister nuclei, and one sees three cells at each pole of 

 the sac. Two of these cells, viz., those formed from the nucleus 

 whose cell-plate was laid down parallel to the longitudinal axis of 

 the sac, remain in position, and are accompanied by the deeper- 

 lying uppermost result of the laying down of a horizontal cell- 

 plate in the other nucleus. The fourth nucleus at each pole 

 remains free, and, moving towards the centre, the two soon become 

 united, the separate nucleoli being often observable some time 

 afterwards. The two first-mentioned cells not being true germ- 

 cells, although they have hitherto been called *' germinal vesicles," 

 are what we shall call " auxiliary vesicles," or shortly " auxiliaries " 

 ((/ehi'd/innen), since, as we shall afterwards see, they assist the germ 

 in its development. The deeper-lying third cell is the real repro- 

 ductive unit — the " germinal vesicle " or '* germ " (ei). The three 

 cells at the other end of the sac which, by-the-bye, are in the 

 same horizontal plane, are of course the " antipodal vesicles." 

 We thus see that everything takes place in a beautifully simj)le and 

 consecutive manner, and that we are released from the necessity 

 of calling in the aid of " free-cell formation," a process which 

 has so often been brought on the tapis to explain phenomena 

 difficult of observation. 



The auxiliaries differ from the germ in being more pointed, and 

 their nucleus is situated at the upper part, the lower being 

 vacuolate, positions which are reversed in the germ. 



For Dicotyledons the author chose Monotropa Hi/jioidti/s, which 

 he found especially suitable for study. The series of changes 

 is essentially the same as in Orchis. Among others Pi/rola, 

 Gloxiiiid }n/hrida, SinniiKjia Lindlei/ana, and especially Torenia 

 asiatica, are commended to the notice of those who wish to see the 

 process for themselves. 



One would naturally expect to find exceptions to the above- 

 sketched series of phenomena, even did one not know that such 

 have been before noticed. The principal ones recorded by Stras- 

 burger are — occasional abortion of the germ in Monotropa, multipli- 

 cation of antipodal vesicles in Ornithoyalam, large cellulose- 



