Nichols, A morphologi'cal study of Juniperus communis rar. depressa. 225 



Division of the central cell nncleus. — About three 

 days before fertilization the nucleus of the central cell divides, 

 giving rise to the ventral canal nuclens and the egg nucleus. 

 Strasburger (1879) figures the spindle of this division in J. vir- 

 yiniana, and it has recently been described in -/. communis by 

 Noren (1904. 1907) and Sludsky (1905). Up to this time the 

 central cell nucleus has exhibited no unusual structural peculiarities 

 It possesses a delicate reticulum in which dark staining masses 

 and irregulär, light staining threads are discernible and has a well 

 defined nucleolus (fig. 79j. As the nucleus approaches division 

 more or less continuous, comparatively thick threads arise in which 

 a distinction between chromatin granules and linin is apparent 

 (figs. 80, 81), and at the same time the nucleolus tends to stain 

 less deeply and reveals a vacuolate structure (fig. 93). 



Coincident with these changes within the nucleus the nuclear 

 membrane on the surface toward the asteroid becomes pressed or 

 drawn inward in the manner shown by figs. 80 and 81, while 

 delicate granulär radiations extend between the center of the 

 asteroid and the invagination thus formed. The first impression is 

 that these radiations represent fibers pressing into the nuclear 

 cavity, but the careful examination of a large number of pre- 

 parations has failecl to reveal any actual connection between them 

 and the spindle fibers eventually formed. Similar phenomena 

 have been variously interpreted by different writers. Murrill 

 (1900) finds that in Tsuga the spindle fibers, arising within a fibrous 

 mass beneath the nucleus "grow upward against and press in the 

 nuclear membrane", and that the membrane then "disappears below, 

 and the spindle fibers press into the nuclear cavity". Miyake 

 (1903 a) reports that in Picea "the spindle fibers first arise from a 

 clear court along the lower side of the nucleus and grow into the 

 nuclear cavity", pressing in the nuclear membrane in the manner 

 described by Murrill. Miss Ferguson (1901) also describes a 

 clear region with delicate granulär threads along the lower half of 

 the nucleus in Pinus, and an irregulär indentation of the upper 

 and lower surfaces of the nucleus, but she fails to ascertain whether 

 any of the threads enter the nuclear cavity and contribute to the 

 formation of the spindle, while Coker (1903b) concludes that in 

 Taxodium the spindle fibers are almost entirely of nuclear origin. 

 Of course, if such is the case, as Miss Ferguson remarks, "the 

 cytoplasmic activity in connection with this division would be in- 

 explicabie". Xevertheless, in the light of the writer's observations, 

 the asteroid does not appear to contribute to the formation of the 

 spindle, and its only apparent use in Juniperus is to form a support 

 for the free lower pole of the spindle, a function already suggested 

 by Mu-rrill (1900). 



The division of the central cell nucleus is consummated 

 rapidly and takes place almost simultaneously in all the archegonia 

 of a group. In one ovule, for example, eight such nuclei were found 

 undergoing division. With the formation of a continuous spirem 

 the distinction between chromatin and linin disappears, and the 



Beihefte Bot. Centralbl. Bd. XXV. Abt. I. Heft 2. 15 



