746 RECORD OF CURRENT RESEARCHES RELATING TO 



body is divided into two halves by a groove, and the hinder half is 

 provided with a flagellum ; the anterior edge of the groove carries 

 fine, short, and closely approximated cilia, and the groove is, on the 

 ventral surface, crossed by a non-ciliated longitudinal groove, which 

 extends along the more posterior region, and the flagellum, when at 

 rest, lies in this groove. These and other details were distinctly 

 made out in small transparent forms, which have hitherto been 

 regarded as Gymnodinium. Examined during growth, the carapace 

 was observed to lose its simple character and to become plated, 

 forming at last some five-and-twenty pentagonal pieces, which were 

 connected together by the new cuticle, which could be seen between 

 them ; this is the form of Peridinium, and in this stage the creature 

 was observed to be sexually mature. The double contour of the 

 covering plates, which may be sometimes observed, is shown to be due 

 to one plate underlying another, and as having been formed into 

 a plate by a bursting of the cortical portion subsequent to that by 

 which the first set of pentagonal plates was formed. 



BOTANY. 

 A. GENERAL, including Embryology and Histology 

 of the Phanerogamia. 

 Division of the Pollen-grain in Angiosperms.* — Botanists havo 

 hitherto generally believed that the processes which take place within 

 the pollen-grain before pollination are essentially different in Angio- 

 sperms and Gymuosperms. In Gymnosperms it has long been known 

 that a division takes place of the contents of the pollen-grain into 

 one large cell from which the pollen-tube is produced, and several 

 smaller cells which take no part in any further process, and have hence 

 been called vegetative cells. An analogy is thus traced with the de- 

 velopment of the microspore of Isoetes and Selaginella, the large fertile 

 cell being regarded as homologous with the antheridium, the vegetative 

 cells with the male prothallium. In Angiosperms, on the contrary, 

 it was believed that the pollen-grain remained perfectly unicellular 

 up to the time of pollination. It is true that Eeichenbach and 

 Hartig detected and figured pollen-grains with two nuclei, a structure 

 which was confirmed by Strasburger. But it has been reserved for 

 F. Elfviug, of Helsingfors, in a most careful and admirable series of 

 experiments carried on in Strasburger's laboratory at Jena, to demon- 

 strate for the first time that a cell-division takes place normally with- 

 in the pollen-grain in Angiosperms corresponding to that of Gymno- 

 sperms. The following are the main results arrived at : — 



At a certain stage of development, before pollination, the pollen- 

 grain of Angiosperms divides into two cells, a larger and a smaller 

 one ; the latter, or " vegetative " cell, may again divide into a two- or 

 three-celled body. 



This latter vegetative cell (or cells) is separated from the large cell 

 only by a protoplasmic membrane, though in a few cases a distinct 

 wall (of cellulose ?) is formed. 



* ' Jenaische Zeitschr. Naturwiss.,' xiii. (1870) \>. 1. 



