**6. Concluding remarks**

In the last three decades, a new approach to understanding the evolution and development of organismic structure diversity has grown into a striking discipline called "evolutionary developmental biology" (EvoDevo) widely using advancements and ideas of molecular biology and genetics, including genomics, transcriptomics, and proteomics, as well as bioinformatics [18, 150–154]. At the same time, comparative plant morphology is quite rightly emphasized should be a valuable sub-discipline of EvoDevo [18, 153]. In the broad sense, EvoDevo comprises form and structure at all organizational levels, i.e. "the form and structure of whole plants, organs, tissues, cells, cell organelles, molecules, etc. and it continues to play a major role in evolutionary biology" [155]. The most striking example of using the traits of of the micromorphology of the androeсium and gynoecium, seeds and fruits, as well as the types of microsporangia, pollen grains, ovules, male and female gametophytes, endosperm, etc. is a new version

of the Takhtajan's phylogenetic system of magnoliophyta [11]. In his opinion, evolutionary taxonomy should be based not only on cladistics analysis, but also on the rates and modes of evolution of individual groups, the degree of their divergence and the level of specialization.

Evolutionary transformations of embryological structures in the general directions and modes of progressive evolution and specialization reveal also the nature of new correlative connections as a result of the indirect influence of the external environment and their changes in the process of evolution. In the evolution of embryological structures there are, on the one hand, complicated correlative connections, on the other hand, more clearly general cellular patterns, i.e. mechanisms of mitosis, cytokinesis, polarity. Such a statement associates primarily with the function of these structures, providing direct plant seed reproduction, and their position as internal structures of generative organs and, consequently, their greatest conservatism in comparison with plant vegetative organs.

It seems expedient to study the mutational and phenotypic variation of the internal structures of angiosperms and the specificity of natural selection of mutations in these structures, which ensure the species reproduction, in particular the stabilizing role of selection. Many mutational changes in embryological structures cannot become the basis for the emergence of stable types if they negatively affect fertility. The limitations imposed by the selection of only those mutations that do not reduce fertility are one of the reasons for the widespread parallelism in the evolution of embryological structures. The specialization of embryological structures at the tissue and cellular levels in the direction of optimizing the implementation of their functions leads to convergent similarity, which manifests itself at these levels in the form of tissue specificity.

It is quite clear that the use of the achievements of molecular biology and genetics should be very fruitful in solving the problems facing evolutionary embryology – the knowledge of the laws of the emergence and historic development of the internal structures of generative organs. Cognition of the gene families and gene regulatory networks underlying development of male and female gametophytes and double fertilization in extant plants will be new insights into understanding pathways of their reproductive evolution. Although the final solution to these issues is still far away, the establishment of new concrete truths at various structural levels of the organization of plant organisms, expanding the boundaries of knowledge and confirming the achieved or refuting it, inevitably raises new debatable questions in such a complex, but extremely interesting and inexhaustible problem as the problem of the history and evolution of plant forms.

*Evolutionary Patterns of the Internal Structures of Generative Organs in Angiosperm Plants DOI: http://dx.doi.org/10.5772/intechopen.100593*
