168 EMBRYOGENESIS IN PLANTS 



to the view that it is an organ which is formed 'only where it is required 

 for the first stages of development and nutrition of the embryo.' 

 Goebel (1898, 1905) had already stated (i) that the relative positions of 

 the primary organs (shoot, leaf, root and foot or haustorium) are not 

 the same in all vascular plants, (ii) that external factors do not determine 

 the early embryonic developments, (iii) that the arrangement of parts 

 is due to internal factors, and (iv) that the positions of the primary 

 organs are such as to be the most appropriate for their function. The 

 essentially organographic view expressed in (iv) was not fully acceptable 

 to Bower: he considered that embryos do not show the plasticity 

 implied in GoebeFs statement. In the development of all pteridophyte 

 embryos (and indeed of all plant embryos). Bower regarded the 

 formation of a polarised filament, spindle or axial body, as the pre- 

 vailing and presumably obligatory initial condition— a development 

 'based on the ukimate type of a transversely septate filament' (1923, 

 p. 301). He did not consider that all the developments observed in 

 fern and lycopod embryos are such as to be 'the most beneficial for 

 their function' : on the contrary he held that some of them, e.g. the 

 formation of a suspensor, reflect a somewhat unprogressive hereditary 

 constitution and impose more or less severe handicaps on the young 

 sporophyte. The reality of the alleged disadvantages may be question- 

 able. Such conceptions are difficult to test scientifically and it will 

 probably remain largely a matter of opinion whether or not a suspensor 

 is a drawback to the developing embryo. Its presence in the embryo of 

 seed plants suggests that if it does not possess functional importance, 

 it is at least not detrimental. 



The Suspensor. When the morphologist asserts that the suspensor 

 is a primitive organ found in some modern survivors of ancient stocks, 

 it may well be that he has seized upon a truth. It is a genetical character 

 which happens to become manifest in the early embryogeny and in the 

 determination of which only a few genes may be specially involved. The 

 genie action which leads to the formation of the suspensor may possibly 

 be seen in those differential protoplasmic changes which occur in the 

 elongating zygote. Even if we accept the view that physical factors 

 determine the way in which a zygote divides, the metabolic material 

 which generates some of the forces, and on which forces must work, is 

 a specific protoplasm in a specific prothallial matrix. 



Comparison of Embryogeny within the Filicineae. If we accept the 

 view that the ferns are a varied but essentially coherent group — a 

 'brush' of phyletic lines originating in a common ancestral group, as 

 Bower described them — it is cogent to consider what community or 

 diversity of organisation they show in their embryogeny. Already we 

 have seen that both in Lycopodium and Selaginella there may be 



