108 The American Naturalist. [February, 



G'tigiKwF* 1 and WiJchman's - Recent Discoveries. — It is not 

 until very recently that anything similar to the asters or archo- 

 plasm has been discovered in the vegetable cell. This year 

 Guignard, a careful observer, published his observations " On 

 the Existence of Attractive Spheres in the Vegetable Cell" 

 which, from present appearances, marks an epoch in the devel- 

 opment of vegetable cytology. 



In the resting nucleus, according to Guignard, two attractive 

 spheres or asters are present. They lie close together at one side 

 of the nucleus, (figs. 49, 54 and 56). Within each is a cen- 

 tral corpuscle, the centrosome (figs. 12, a, 49, 54, etc.) surrounded 

 by a transparent areole and around this a granular circle (fig. 

 12 b.). In general the radiating striae are invisible as long as 

 the cell is in a state of repose (fig. 49). They become feebly 

 apparent when the nucleus presents the first symptoms of en- 

 tering upon division and at this time they withdraw from each 

 other in order to place themselves at two opposite points cor- 

 responding to the poles of the future spindle (figs. 12 and 51). 

 After this the striae become more evident and direct themselves 

 toward the nucleus, while it is still provided with a nuclear 

 membrane, which confirms the opinion of Strasburger that the 

 spindle originates outside the nucleus in the cytoplasm. When 

 the chromatin segments have separated and collected at the 

 poles, the centrosomes divide in each sphere into two new cen- 

 trosomes, which thus have their origin at each pole (figs. 53 and 

 55). They remain in this position till the next nuclear divi- 

 sion is preparing to start, when they separate as explained 

 above. 



" In resume," says Guignard, "the bodies in question, which 

 merit the name of directive spheres since they govern the divi- 

 sion of the nucleus, transmit themselves without discontinuity 

 from one cell to the other throughout the life of the plant," 



1 Leon Guignard, " Sur 1* Existence des ' Spheres Attractives ' dans les Cellules 

 Vegetates." Compt. Rend. Soc. de Biol. T.iii; p. 182. (March 20, 1891).— Ann. 

 des Sci. Nat. Bot. T. xiv; No's. 3-4; pp. 163-288 (Nov. 1891), (10 pi.). Comptes 

 rendus Acad, des Sci., 9 Mars 1891. 



2 E. De Wildeman, in Bull. Acad. Roy. Sci. Belgique, LXI (1891) pp. 594-602 

 (lpl.) 



