THE ANGiOSPERMAE 1463 



framework holding the reserve materials and destined to complete solution 

 at the time of germination. 



Aggression by the endosperm on the integuments may lead to " rumi- 

 nation " or infolding of the two sets of tissues, which we shall refer to in the 

 next chapter. It may go so far as to destroy the integuments completely, as 

 in Crinum, where the outer layers of the endosperm become suberized and 

 form a secondary covering layer to the seed. 



The Development of the Embryo 



Plant embryology long suffered neglect. The principal reason probably 

 was that the earlier studies did not offer much prospect of contributions 

 to the history of evolution parallel to those which had distinguished verte- 

 brate embryology. Fifty years ago it was the habit of botanical lecturers to 

 dismiss the angiospermic embryo as a relatively slight and simple structure, 

 which had been so influenced and conditioned by its environment that it 

 offered no indications of its phylogeny and was therefore (according to the 

 ideas of the day) of little interest. The time has long gone by when it was 

 possible to speak of a " typical " dicotyledonous or monocotyledonous 

 embryo, for the great diversity revealed by extended embryological study 

 has clearly shown that there is no such thing. 



Embryology now embodies an immense amount of detailed comparative 

 information and in the hands of a group of devoted investigators it has 

 expanded into an important region of botanical knowledge. Into the details 

 of the subject it is impossible to enter here. We must be content to indicate 

 a few general principles. For a grand marshalling of the information we must 

 refer readers in the first place to " Plant Embryology " by Dr. A. Johansen 

 (Chronica Botanica Co., 1950) or to " Embryologie der Angiospermen " by 

 Karl Schnarf (Borntraeger, 1927-9), or to the more concise review in " An 

 Introduction to the Embryology of Angiosperms ", by P. Maheshwari 

 (McGraw-Hill, 1950). 



Johansen rejects consideration of the many ancillary aspects of embryo 

 formation, such as the building of the female gametophyte, fertilization, 

 the endosperm development and so on which we have been hitherto dealing 

 with, and concentrates attention on the embryo itself, from various points 

 of view; i.e., its origin (embryogenesis), its architecture (embryotectonics), 

 its destination and functions (embryogenergy) and lastly the laws of embryo- 

 nic development (embryonomy). The second and the last of these aspects 

 make up the core of the subject and they are sufficiently wide to warrant his 

 extensive treatment. So great is the diversity in embryo building that 

 Johansen does not separate Dicotyledons and Monocotyledons as distinct 

 groups from the embryological point of view, for there is no general embryo- 

 logical distinction between them, at least in the important early stages. 



The first practical scheme of classification of embryos into develop- 

 mental types was made by Schnarf in 1928. He recognized five Types of 

 development among Dicotyledons and named them after families in which 

 o* 



