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INTRODUCTION TO EMBRYOLOGY OF ANGIOSFERMS 



stony endocarp with two to four upwardly directed prongs repre- 

 senting the persistent sepals. 



Callitrichaceae. The genus Callitriche comprises about 25 species, 

 which are extremely reduced in both vegetative and floral struc- 

 ture. The male flower consists of a single terminal stamen, and the 



CD E G< 



Fig. 200. Development of embryo sac and embryo in Trapa. A, megaspore 

 mother cell in synizesis. B, same, undergoing first meiotic division. C, tetrad 

 of megaspores. D, two-nucleate embryo sac with three nonfunctioning megaspores. 

 E, upper part of mature embryo sac. F,G, two consecutive sections through lower 

 part of embryo sac, showing hypertrophied and degenerating antipodal nuclei. 

 (After Ishikawa, 1918.) H, diagrammatic l.s. of young seed, showing two integu- 

 ments, massive suspensor, and embryo. (After Tison, 1919.) 



female of a short-stalked bicarpellary ovary situated between a 

 pair of delicate bracteoles. Each cell of the ovary becomes divided 

 by a false septum, and there is a single pendulous anatropous ovule 

 in each of the four loculi. There is a pair of long styles placed 

 transversely like the carpels. 



The exact position of Callitriche has always been considered 

 doubtful. According to Bentham and Hooker, R. Brown, De 

 Candolle, and Hegelmaier and Hutchinson, it is related to the 

 Halorrhagidaceae ; Clarke (1865) recommended that it should be 

 placed under the Caryophyllaceae ; and Baillon (1858) included i> 



