1430 A TEXTBOOK OF THEORETICAL BOTANY 



This view is strengthened by various anomalous occurrences. For 

 example, cases of reversed polarity are known, e.g., in Woodfordia (Lyth- 

 raceae) and Ulmus americana where the antipodals are organized as an egg- 

 apparatus and the micropylar group have the appearance of antipodals. In 

 Balanophora indica the embryo sac has a horseshoe form, with the oosphere 

 group at one end and the antipodals at the other, in close proximity. 

 According to Van Tieghem either group may be fertilized by the pollen 

 tube. Fertilization of an antipodal cell by a male nucleus has also been seen 

 in Nigella arvensis but there is no proof that such anomalous fertilization 

 can produce a mature embryo. It is said that Criniim may have an egg- 

 apparatus at both ends of the sac, and there are several observations of 

 antipodal cells simulating synergids, even to the possession of a filiform 

 apparatus. (See Fig. 1313A.) 



The comparison of the egg-apparatus of an Angiosperm with a simple 

 type of gymnospermic archegonium, like that of Torreya, is shown in 

 Porsch's diagram here reproduced (Fig. 13 18). The interpretation of the 

 synergidae as neck cells, which was earlier supported by Guignard and by 

 Treub, is argued by Porsch on the ground that in Gymnosperms (except 

 in Gnetales) the archegonium is never reduced beyond four cells: two neck 

 cells, the ventral cell or oosphere and the ventral canal cell, though the 

 existence of the latter in Torreya taxifolia is doubtful, unless it is rapidly 

 expelled from the oosphere. At least two neck cells are invariably formed. 

 The alternatives to Porsch's view are that the synergidae are prothallial or 

 that they are potential oospheres. The former suggestion we have already 

 dealt with. Instances of the fertilization of synergid cells would be expected, 

 if the latter suggestion were correct, and some have been recorded, but on 

 the basis of embryos having been seen developing from these cells. These 

 are almost certainly cases of the widespread phenomenon of polyembryony. 

 Diploid, unreduced embryo sacs frequently occur, in which any, or several, 

 of the nuclei may divide and produce embryos. Even in haploid sacs, 

 haploid embryos may arise, but in none of these cases is there any fertili- 

 zation involved in their formation. In fact, in view of the well-established 

 cases in which it is known that the pollen tube enters and discharges its 

 generative nuclei into and through a synergid, followed by normal fertiliza- 

 tion of oosphere and endosperm nucleus, it is reasonable to conclude that 

 synergid nuclei are not equivalent to egg-nuclei and are not fertilizable. 



When we survey the various theories of the embryo sac outlined above, 

 it is difficult to halt between the first and the last, which is open to fewer 

 objections than the others. One item of evidence, not hitherto mentioned, 

 may be cited from Torreya. Anomalous embryo sacs have been noticed in 

 which two archegonia occur and, instead of lying side by side as in most 

 Gymnosperms, they are situated at opposite ends of the sac, in just the 

 position that Porsch believes them to be placed in the Angiosperms. 



Berridge has criticized the Porsch theory on the ground of the improba- 

 bility of the ventral canal nucleus exhibiting the activity and the sexual 

 character shown by the upper polar nucleus in Angiosperms. She has put 



