Nichols, A morphological study of Juniperus communis var. depressa. 207 



and in close contact, either parallel or twisted around each other 

 corkscrew-fashion, but frequently they are in contact at only one 

 or two points. 



Coincident with these nuclear metamorphoses, changes have 

 been taking place in the cells themselves. They have lost their 

 angular shape and compact arrangement and have become more or 

 less separated from one another (fig - . 11). This Separation is 

 apparently brought about by the dissolution of the middle lamella 

 of the mother cell in the manner described by Strasburger (1882). 

 Allen (1905) reports an interesting process in connection with the 

 Separation of the pollen mother cells in Lilium ccmadense. There 

 the wall of the mother cell dissolves, leaving the cells protected 

 only by a plasma membrane, and subsecpiently an entirely new 

 wall is developed about the cell. In Juniperus, immediately after 

 the Separation of the mother cells, the wall appears very thin, but 

 at all times places may be found where the cytoplasm has shrunk 

 away from the surrounding membrane, which would hardly be true 

 if the cells were surrounded merely by a differentiated layer of 

 cytoplasm. 



Up to this time the cytoplasm has exhibited afairly uniform 

 alveolar structure. As the nucleus emerges from synapsis, however, 

 a fiber-like, radial arrangement of the cytoplasmic materials is 

 faintly discernible (fig. 20), similar to that figured in the pollen 

 mother cells of Lilium by Mottier (1897, fig. 3), and in Larix 

 by Allen (1903, fig. 6). Shortly before diakinesis there is evident 

 a concentration of the cytoplasm toward the nucleus, and by the 

 time the segmentation of the spirem has taken place the nucleus 

 is enclosed by a dense granulär layer, while toward the periphery 

 of the cell the cytoplasm has become thin and stains very lightly 

 (fig. 21). This dense layer of cytoplasm around the nucleus doubt- 

 less represents the 'felted' structure described in Larix by Bela- 

 jeff (1894), Strasburger (1895), and Allen (1903), but on account 

 of the small size of the cells it is impossible to ascertain definitely 

 its nature here. Occasional indications are seen, however, of 

 a fibrous structure like that described by the above mentioned 

 authors. 



The nuclear membrane, which until now has been sharply 

 outlined, disappears soon after the formation of the 'feit', and the 

 dense cytoplasmic layer appears to press into the nuclear cavity. 

 The origin of the spindle fibers, however, cannot be clearly de- 

 monstrated. Osterhout (1897) and Mottier (1897) find that during 

 diakinesis, in the species which they studied, fibers of unmistakably 

 nuclear origin become attached to the chromosomes. But a careful 

 study of the chromosomes of Juniperus before the dissolution of 

 the nuclear membrane has failed to reveal any such structure, 

 and it is impossible to state whether the spindle fibers are derived 

 entirely from the cytoplasm or whether they originate partly within 

 the nucleus. 



The spindle when first formed is multipolar (fig. 24), but 

 rapidly resolves itself into a multipolar diarch (fig. 25), and 



