INVEKTEBRATA, CRYPTOGAMIA, MICROSCOPY, ETC. 903 



passing over the one into the other. Although minor differences were 

 observed in the course of development even in the same plant, the final 

 result was the same ; that the first separation of the three primary- 

 layers is brought about in this way, that in an optical transverse section 

 of the embryo each of its constituent quadrants appears to be comj^osed 

 of an inner plerome-cell, two periblem-cells, and two dermatogen- 

 cells. 



2. The second important result, both in Alisma and Capsella, is 

 that the cotyledons — as to whose foliar nature no doubt has been 

 entertained — cannot be regarded, as is the case with the other foliar 

 organs, as outgrowths of the dermatogen and the periblem of the axial 

 portion of the embryo. The cells from which the three primary 

 layers which compose them originate, are of altogether equal value 

 with those of the axial portion. In both plants the two inner of the 

 primary layers do not originate by outgrowth from the layer already 

 formed and differentiated in the axial portion, but by division, by walls 

 parallel to the surface, of the layer which lies beneath the dermatogen 

 in the upper half of the embryo. The divisions which give rise to the 

 three primary layers, as well as those which afterwards arise in these 

 layers, are altogether of equal value in both parts of the embryo, and 

 correspond with one another. 



3. The first division walls in the embryo of Alisma are transverse, 

 and are formed successively in strictly basipetal order. To the first 

 three walls the three principal portions of the future embryo — the 

 cotyledon, the central portion, and the root — owe their origin, and they 

 remain completely differentiated during the whole course of its 

 development. The uppermost cell gives birth to the cotyledon, the 

 second to the central portion, on which the stem-bud (plumule) is 

 formed, the third to the root ; by the transverse divisions which 

 follow, the hyjiojihysis and a portion of the pro-embryo (suspensor) 

 are formed. 



4. The place of origin was accurately determined by the detection 

 of two dermatogen-cells in the central portion of the embryo, which 

 were readily distinguished from the other superficial cells of this 

 layer both by their form and by the divisions which occur in them. 



5. In Capsella the differentiation of the tissue in the growing 

 cotyledons in the earliest stages of their development, and the cell- 

 divisions in the pro-embryo, must be regarded as new. 



Development of the Embryo-sac of Angiosperms.*— M. Vesque, 

 in a further communication on this subject, considers that the recent 

 discovery of Strasburger fills uj) a space which i:)reviously appeared 

 to separate Phanerogams from Vascular Cryptogams, According to 

 the recent observations of the author, the primordial mother-cell of 

 the embryo-sac, as defined by Warming, divides, by transverse septa, 

 into two, three, four, or five special mother-cells, the homologues of 

 the mother-cells of the pollen of Phanerogams, or of the spores of 

 Vascular Cryptogams. These septa are formed in succession from 

 below upwards, or from above downwards, according as the primordial 



* 'Comptes Reudus,' Ixxxviii. (1879) p. 1350; aud 'Anu. Sci. Nat. (Bot.),' 

 viii. (1879) p. 261. 



