416 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



themselves should have escaped all reduction, for they still main- 

 tain the same essential structures seen in the gymno sperms, being 

 provided with neck cells as well as a ventral canal nucleus. 2 In- 

 deed, from this point of view, Gnetum and Welwitschia must be 

 regarded as more advanced than the angiosperms, for they have 

 no differentiated archegonia nor any other structures which can 

 be interpreted as archegonia in terms of Porsch's hypothesis. 



2. In all archegonia of the pteridophytes and gymnosperms the 

 ventral canal nucleus is situated directly above the egg. In angio- 

 sperms, on the contrary, the upper nucleus, which should have 

 formed the ventral canal cell, is supposed to have given rise to the 

 egg, while the lower, which should have organized into the egg, is 

 said to represent the ventral canal nucleus! The question also 

 arises as to why the ventral canal nuclei belonging to two different 

 archegonia, one micropylar and the other chalazal, should jointly 

 fuse with a male gamete to give rise to the endosperm, while the 

 egg cell (i.e., the central antipodal cell) belonging to the chalazal 

 archegonium ordinarily exercises no attraction whatsoever toward 

 the second sperm. Normally, the ventral canal nucleus is an inert 

 structure, which is already disorganized at the time the egg is ready 

 for fertilization, and even in those gymnosperms in which it is 

 incidentally fertilized, the fusion nucleus does not undergo more 

 than a very few abortive divisions. 



3. In the angiosperms there are several known instances of em- 

 bryos arising from synergids, either as the result of fertilization 

 or even without it. There is no recorded instance, however, where 

 the neck cell of a true archegonium has behaved in a similar fash- 

 ion. Since the embryo sac of angiosperms is a more reduced struc- 

 ture than that of gymnosperms, it seems rather strange that the 

 "neck cells" of the archegonium, which are headed toward extinc- 

 tion (they are already extinct in the embryo sacs of Plumbago and 

 Plumbagella) , should become egg-like and produce rival embryos. 



4. In some species of Peperomia and in Acalypha indica the egg 

 is associated with a single synergid. Must we then suppose that 

 here we have an archegonium in which one neck cell has disap- 

 peared, leaving the other to carry on the function of both? 



5. A fifth objection is that the components of the chalazal quar- 



2 Even in the conifers there are some genera which do not have a ventral canal 

 nucleus (Chamberlain, 1935). 



