Nichols, A morphological study of Juniperus communis var. depressa. 205 



a pairing of the chromatic material is present in the nucleus of 

 the resting mother cell of the form under consideration the writer 

 is unable to make it out. Nor is it possible to recognize in the 

 nucleus, either at this time or during the subsequent stages leading 

 up to the formation of microspores, a sharp distinction between 

 chromatin and linin, such as is present in the nucleus of the body 

 cell just before its division. In view, however, of the small size 

 of these nuclei this fact by no means preeludes the probability that 

 such a differentiation may be present. 



One or more large nucleoli are conspicuous in the nucleus. 

 The cytoplasin is uniformly distributed through the cell, and in 

 most cases presents merely a granulär appearance; but in well 

 prepared sections a distinct alveolar structure is evident, the contour 

 of the non-staining "alveolar spheres" being outlined by the thickly 

 scattered microsomes (see Wilson 1900, p. 46). Minute, glistening 

 granules of starch are present in the cytoplasm, and these are 

 more or less prominent during the succeeding stages of development. 



Tetrad division. — The behavior of the chromatic material 

 in the nuclei of the microspore mother cells during the early pro- 

 phase of the heterotypic division is very similar to that described 

 by Allen (1905) in the pollen mother cells of Lüium canadense. 

 As the nucleus approaches synapsis the n'ner threads of the chro- 

 matic network are drawn in, the material of the knots shows a ten- 

 dency to become distributed along the coarser connecting Strands, 

 and the reticular structure gradually gives way to a series of more 

 or less united, lumpy bands. At the same time it becomes evident, 

 as shown in figs. 16 and 17, that in many places separate Strands 

 or masses of chromatin have come to lie alongside one another. 

 Sometimes they approach so close that they appear to have united, 

 but again it can be made out that there are two distinct Strands 

 lying side by side. Coincident with these changes the chromatin 

 begins to aggregate toward the central region of the nucleus, and 

 a heaping up of the nuclear materials begins. This continues until 

 a mass of tightly interwoven Strands is formed which moves to one 

 side of the nuclear cavity and assumes a position close to the nuclear 

 membrane (fig. 18). Just what conditions prevail during synapsis 

 it is impossible to make out with certainty. Occasionally, however, 

 threads are found which project out from the almost homogeneous 

 mass, and from the appearance of these, and in view of the pre- 

 ceeding and subsequent phenomena, it may be inferred that there 

 is present at first a series of double threads, and that toward the 

 close of synapsis these coalesce and unite end to end to form a 

 single bivalent spirem. There appears to be no rule as to which 

 side of the nuclear cavity the synaptic mass occupies (fig. 10). 

 The nucleoli in most cases protrude from the chromatic ball and 

 occasionally are entirely extruded, but they never exhibit the 

 flattened appearance described by Allen (1905). 



Considerable theoretical interest is attached to the view held 

 by several eminent cytologists, among them Berghs (1904, 1905), 

 Allen (1905), and Overton (1905), that there is a presynaptic 



