220 Nichols, A morphological study of Juniperus communis var. dcpressa. 



gerne division (fig. 67). In two of the cells figured, one of the 

 daughter nuclei of the first division has redivided, while in the 

 other the heterotypic division has just been completed. Whether 

 more than one of the functional megaspores thns formed would 

 have developed further cannot, of course, be stated, but it is not 

 unlikely, since Sludsky (1905) reports that in the European form 

 he twice found two endosperms in a Single nucellus. In connection 

 with these abnormal cases it is interesting to note that here, as 

 in Cryptomeria (Lawson 1904b). two megasporangia occasionally 

 oeeur within a Single integument. 



During the division of the megaspore mother cell there is 

 present just below the nucleus the conspieuous kinoplasmic body 

 (figs. 63, 66, 67) which Noren (1907) has described in the European 

 form. Analogous struetures have been noted in the megaspore 

 mother cells of Taxodium, Thuja, and Taxus (Coker 1903, 1904), 

 and Torreya (Eobertson 1904a). Its significance is still a matter 

 for discussion, but it may be worthy of mention that the writer 

 has observed very similar bodies in the later stages of prothallial 

 development (fig. 77). 



Immediately following the homotypic division the functional 

 megaspore becomes cut off by a membrane and enlarges until'it 

 fills the entire space originally oecupied by the mother cell (figs. 

 68, 69), while the nuclei of the non-functional cells rapidly dis- 

 organize and are eventually absorbed. 



The female gametophyte. 



Development of the prothallium. — The observations 

 of Noren (1907) on the development of the female gametophyte, 

 briefly stated, are as follows: The megaspore germinates rapidly 

 and gives rise to an embryo sac containing a large central vacuole 

 and numerous free nuclei imbedded in a peripheral layer of cyto- 

 plasm. Nuclear division takes place simultan eously throughout the 

 sac. In the development of the prothallium open tubes are formed 

 which grow in toward the center of the embryo sac in the 

 manner first described by Mlle. Sokolowa (1890). The nucleus 

 of each tube then divides, and cross walls are laid down. The 

 megaspore membrane consists of two distinet layers. Noren's 

 observations are for the most part confirmed by those of the 

 writer. 



The development of the embryo sac from megaspore to multi- 

 cellular prothallium oecupies about five weeks. During the few days 

 following its differentiation the megaspore increases very little in 

 size, but the primary nucleus undergoes its first division. 

 The two resultant nuclei oecupy a central position, and the cell 

 contains several small vacuoles. With the advent of the four 

 nucleate stage the small vacuoles flow together to form one large 

 central vacuole, and the cytoplasm with its included nuclei comes 



