EMBRYOLOGY IN RELATION TO TAXONOMY 



363 



minute air space between the two integuments in the chalazal region 

 of the ovules of Pereskia (Fig. 199.4) and Opuntia (Neumann, 1935; 

 Archibald, 1939). This has also been noted since then in several 

 members of the Centrospermae. A radial elongation of the terminal 

 cells of the nucellar epidermis, followed by some periclinal divisions 

 in later stages (Fig. 199(7), is common to the Aizoaceae and Cac- 

 taceae. Further, some significant similarities of an anatomical 

 nature have recently been recorded between the spiny or scaly 



Fig. 199. Ovary and ovule of Pereskia amapola. A, l.s. young ovule, showing a 

 prominent air space I between inner and outer integuments. B, l.s. pistil showing 

 stylar canal. C, l.s. upper lart of ovule, showing nucellar cap and micropyle formed 

 by inner integument. (After Neumann, 1935.) 



emergences of Pereskia and Rhipsalis (Cactaceae) and Anacamp- 

 seros (Portulacaceae). 4 Present evidence, therefore, seems to be 

 entirely in favor of regarding the Cactaceae as a sort of bridge be- 

 tween the Aizoaceae and Portulacaceae. Among specific simi- 

 larities between the Portulacaceae and Cactaceae, Neumann (1935) 

 cites the following: (1) microspore mother cells forming one to two 

 (only rarely more than two) rows in the anther loculus; (2) micro- 

 pyle in close proximity to the funiculus; (3) T-shaped tetrad of 



4 For details, see Chorinsky (1931). 



