i6o BOTANICAL GAZETTE [august 



Trifolium repens 



This species agrees very closely with Trifolium hybridum. Fig. 

 28 shows the reduction division of the mother cell; n chromosomes 

 are shown, but various counts gave 11 and 12. The number is 

 small, about 12. In fig. 29 one megaspore mother cell has pro- 

 duced 4 megaspores, while the other one has enlarged but has made 

 no division. The third megaspore often functions (fig. 30). The 

 embryo does not differ from that of Trifolium hybridum. The 

 endosperm masses about the embryo in its early development, but 

 no walls occur. Not much sterilization was observed. 



Medicago sativa 



In Medicago sativa the number of ovules in an ovary varies 

 considerably, ranging between 12 and 18. The nucellus is more 

 massive than that of Trifolium. The number of subepidermal 

 rows ranges from 5 to 7 (figs. 31, 34). The outer integument pre- 

 cedes the inner as in Trifolium. The number of archesporial cells 

 ranges from 1 to 6, and more than one usually occurs (fig. 31). 

 One parietal cell is nearly always cut off, but occasionally mega- 

 spore mother cells may be found with no parietal cells (fig. 32). 

 The parietal cell usually makes only one division, which is trans- 

 verse (figs. 32, 33), but at times the transverse division is followed 

 by one or more longitudinal ones (fig. 34). Prominent cell plates 

 accompany the formation of the megaspores (figs. 33, 34). From 

 2 to 4 rows of megaspores may occur in the same nucellus (fig. 34) 

 and often more than one megaspore starts to form an embryo sac 

 (fig- 35) j but not more than one mature sac was found. The 

 embryo sac destroys the surrounding nucellar tissue more uni- 

 formly and does not become so tubular as in Trifolium (figs. 36, 37). 

 The large central vacuole which appears during the formation of 

 the 8 nuclei (fig. 36) disappears later, and the cytoplasm becomes 

 compact and filled with starch (fig. 37). The 8 nuclei of the embryo 

 sac are arranged in two groups of 4 each, separated by the large 

 vacuole (fig. 36), and when the embryo sac is mature, 3 nuclei of 

 each group are definitely set off at the poles in separate masses of 

 cytoplasm, while the 2 polar nuclei occupy the median mass ot 

 cytoplasm (fig. 37). The polars meet near the middle of the sac 



