66 



INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



who first called attention to this 

 patch of cells, gave it the name 

 hypostase, and believed that 

 it formed a sort of barrier or 

 boundary for the growing em- 

 bryo sac and prevented it from 

 pushing into the base of the 

 ovule. Goebel (1933) says, 

 however, that the peculiar po- 

 sition of this tissue — directly 

 above the termination of the 

 vascular supply of the ovule — 

 is indicative of its relation to 

 the water economy of the em- 

 bryo sac. While the function 

 of the hypostase is still in 

 doubt, morphologically it is a 

 very characteristic feature of 

 certain families and genera. 

 Zostera (Dahlgren, 1939) offers 

 an especially good instance of 

 a well-developed hypostase 

 (Fig. 47). The hypostase may 

 not always consist of thick- 

 walled cells. In Knautia (La- 

 vialle, 1925) it comprises a 

 group of small thin-walled cells 

 having a number of schizoge- 

 nous cavities which branch 

 and anastomose and become 

 filled with a yellowish sub- 

 stance, which also spreads into 

 the antipodal cells and other 

 adjacent tissue. In Dionaea 

 (Smith, 1929) some of the thin- 

 walled cells in the chalaza be- 

 come disorganized and replaced 

 Jig. 47. Zosteia marina, l.s. young seed, ° 



showing prominent hypostase and well-de- by airspaces . In A Ilium odorum 

 veloped embryo. (After Dahlgren, 1939.) (Haberlandt, 1923) the cells 



