Nichols, A morphological study of Juniperus communis var. depressa. 217 



matin and linin proper, there is evident in the nucleus a delicate 

 protoplasmic network. The presence here of these three seemingly 

 distinct nuclear elenients in not necessarily at variance with 

 the conditions found in the microspore mother cells, where it is 

 impossible to make out such a differentiation, since many writers, 

 especially among the zoologists, maintain that both "nucleus and 

 cytoplasm have arisen through the differentiation of a common 

 protoplasmic medium" (Wilson 1900, p. 40), and that the various 

 elements in the cell are merely diiferent physiological expressions 

 of the same substance (see also Chamberlain 1899, p. 277). 

 Fig. 56 shows a later stage in the division. The spirem has seg- 

 mented into twelve slender and often twisted chromosomes, while 

 the distinction between chromatin and linin has disappeared. At 

 the same time delicate granulär fibers have arisen in the nucleus. 

 The chromosomes rapidly become shorter and thicker and are 

 oriented at the equatorial plane while the fibers give rise to a 

 blunt, miütipolar diarch spindle (fig. 57), and the nuclear membrane 

 disappears. As shown in the figures, no indications of a fibrillar 

 structure are as yet present in the cytoplasm outside the nucleus, 

 although Sludsky's figure would lead one to look for them. 

 Fig. 58 represents the late telophase of this division. A cell plate 

 has been formed extending entirely across the cell, and the 

 connecting fibers are still evident. The nuclei have reorganized, 

 and the chromatin appears to be in the form of small granules — 

 the psendonucleoli of Noren (1907) — suspended in a network of 

 linin, as was described by Lawson (1904b) in Cryptmneria. 



The megasporangium. 



Development of the megaspore mother cell. — Noren 

 (1907) finds in the European J. communis that soon after polli- 

 nation a group of several cells, the archesporium, becomes re- 

 cognizable in the lower portion of the nucellus, one of which 

 becomes the megaspore mother cell. The non-functioning arche- 

 sporial cells give rise to the tapetum, which surrounds the de- 

 veloping embryo sac and persists until after the formation of the 

 endosperm. The tetrad divisions take place early in the year 

 following the appearance of the archesporium and generally give 

 rise to three cells, one of which is the functional megaspore. 

 During the first of these divisions a reduction in the number of 

 chromosomes is effected in the same manner as in the microspore 

 mother cells. 



The buds which give rise to the pistillate flowers in var. 

 depressa are formed during the latter part of the growing season 

 which precedes pollination. They are borne in the axils of the 

 leaves on branches of the same year. In material collected less 

 than five weeks before pollination it is impossible to distinguish 

 vegetative from flower buds, but four weeks later (May 19) the 

 ovules have begun to develop and present the appearance shown 



