THE ANGIOSPERMAE 



1417 



Fig. 1309. — Deiidrophthoia oracile. A, Longitudinal section of female flower with central 

 " mamelon ", containing two young embryo sacs. B, Mamelon enlarged showing two 

 uninucleate embryo sacs. C, Flower in section showing mature embryo sacs growing 

 upwards through carpellary tissue. Vascular tissue shaded and partly omitted. D, 

 Fusion of lower ends of embryo sacs in the mamelon, forming one tube. E, Embryo sac 

 showing three synergidae, oosphere and degenerating polar nuclei. {After York.) 



gidae, but it descends below them as a rule, so that its lower end, containing 

 the female generative nucleus, appears below the synergidae and gives the 

 impression that the oosphere cell is attached to the base of the synergid cells. 

 It has the shape of a rather stumpy pear, of which the obliquely flattened 

 narrow end is attached to the embryo sac wall, lower than the attachments of 

 the synergidae, and the inner surface forms common faces with both the 

 latter cells. 



The nature of the oosphere membrane is naturally of interest in con- 

 nection with fertilization. Unfortunately these embryo sac cells have such 

 thin membranes that it is not very easy to determine their nature. While 

 cellulose and pectic substances have both been recognized in the synergid 

 walls, there are various opinions about the wall of the oosphere, which, 

 indeed, may not be of uniform nature. Cellulose has been recognized in its 

 upper part, where it is in contact with the synergidae, but the lower, tree, 

 portion seems to have only a plasmatic membrane until after fertilization, 

 when cellulose has been found to appear in it. 



Apart from its nucleus, the possible presence of plastids or plastid 

 rudiments in its cytoplasm is a matter of interest in the oosphere, which is 

 obviously a focal point with regard to the permanence of plastids and their 

 inheritance, which is sometimes matroclinous. Yet direct observations are 



