188 MORPHOLOGY OF ANGIOSPERMS 



. In general, the first division of the fertilized egg is trans- 



verse, and this is followed by one or more divisions in parallel 

 planes, resulting in a row of cells. This undifferentiated group 

 of cells is conveniently referred to as the proembryo. In gen- 

 eral, the proembryo becomes differentiated into suspensor and 

 embryo, which eventually become very distinct, although their 

 origin is variable. This means that in general all the product 

 of the fertilized egg does not enter into the structure of the 

 embryo, a fact also true of most Gymnosperms. In general, 

 the development of the embryo is initiated by the longitudinal 

 division of the end-cell of the proembryo, and this is followed 

 by divisions that result in the quadrant and then the octant 

 stage. It is in the octant stage that periclinal walls may cut off 

 the dermatogen, but this may be deferred to a later stage, and 

 is often irregular. The cells of the dermatogen divide only by 

 anticlinal walls, but the inner cells continue divisions in the 

 three dimensions, and soon the periblem and plerome become 

 distinguishable. In general, the end-cell of the proembryo does 

 not produce all of the embryo, but the next cell divides trans- 

 versely, and the daughter-cell adjacent to the embryo (hypo- 

 physis) fills out the periblem and dermatogen of the root-tip. 

 The organization of the growing points of stem and cotyledon, 

 in relation to the body of the embryo, are so radically different 

 in Monocotyledons and Dicotyledons that no general statement 

 concerning it is possible. 



The fact remains that every general statement given above 

 is contradicted by well-known and bv.Jio means infrequent ex- 

 ceptions, and even the distinction beween^J&onocotyledons and 

 Dicotyledons is not always clear in the embryo. The subject 

 will be treated in some detail under the titles Monocotyledons, 

 Dicotyledons, Parthenogenesis, and Polyembryony. 



MONOCOTYLEDONS 



The embryo of Alisma Plantago, as described by Hanstein 7 

 and Famintzin, 17 has long been taken as a type of the monocot- 

 yledonous embryo. Among recent accounts Schaffner's 43 de- 

 scription of the embryo of Sagittaria varidbilis, following his 

 earlier study of Alisma, is the most complete, and while it 

 confirms the principal features of the earlier accounts, the great 

 improvement in technique since the time of Hanstein made it 



