368 BULLETIN OF THE 



(secondary) disks in place of the nuclei, smaller than the primary disk ; 

 (5.) the disappearance of the secondary disks; (6.) the appearance of 

 four (tertiary) nuclei in positions corresponding to the four angles of a 

 tetrahedron. 



Of the secondary disks, it is further said that their surfaces are either 

 (a) parallel with, or (h) perpendicular to, the Kornerplatte, from which 

 it may be justly inferred that the author mistook in the first case (a) 

 the mutually receding lateral halves of the primary disk for second- 

 ary disks, and that only those having the position indicated under (6) 

 were really secondary structures. He says concerning the latter that 

 they may lie in the same plane, or their planes may be mutually per- 

 pendicular. The latter arrangement evidently corresponds to the tetra- 

 hedral disposition of the four nuclei, which result from the division of 

 these two disks. 



In the Equisetacese (p. 148) "numerous stages of transition between 

 these disks and the spherical cell-nucleus, with respect to the size of the 

 whole structure as well as the rods (Korperchen) which compose it, are 

 observable." 



As Strasburger has already pointed out, Tschistiakoff ('75) w^as the 

 first to observe in plant cells the fibrous differentiation of the nuclear 

 spindle. The account which he {loc. cit., col. 20) gives for the mother 

 cells of the microspores of Isoetes Durieui, is essentially the same as that 

 for Lycopodium and Equisetum (col. 24, 25). In Angiopteris (col. 7), 

 where the spindle figure was not observed, the protoplasm during the 

 division of the cell is entirely homogeneous, without any such morpho- 

 logical differentiation as nucleus and nucleolus. Inasmuch as these are 

 visible when the cell is subjected to the influence of water, he offers 

 the following as an explanation of the phenomena. The plasma un- 

 dergoes several steps of chemical metamorphosis, which begin at the cen- 

 tre of the cell contents. The inner plasm absorb? more water than the 

 more peripheral portions, because it is in a more advanced state of 

 chemical metamorphosis, and thereby the optical properties of the parts 

 become so different that the inner one becomes distinguishable as a nu- 

 cleus, whereas before the action of the water it had no definite bounda- 

 ries. Therefore, nucleus, nucleolus, and primordial utricle are only so 

 many successive steps in the process of metamorphosis.* 



This seems to be very nearly equivalent to saying they have no mor- 



* See also Tschistiakoff, Notice preliminaire sur I'histoire du developpemeiit 

 des sporanges et des spores de I'lsoetes Durieui, Bory. In Nuovo Giornale Botanico 

 Italiano, Tom. V. p. 207. 



