196 



EMBRYOGENESIS IN PLANTS 



type, on the grounds of the abundant occurrence of cleavage poly- 

 embryony, the formation of rosette embryos, and the presence of an 

 apical cell. On the other hand, in Pseudotsuga, there is simple poly- 

 embryony and no single apical cell ; also, there are no rosette cells and 

 therefore no rosette embryos. On these grounds it is recognised as the 



H 



Fig. 43. Comparative series of embryos of Pinaceae 



A, B, Pinus laricio {P. nigra). C, D, Cedrus libani. E, F, Tsuga mertensiana. G, H, 



Pseudolarix amabilis. J, K, Abies balsamea. L, M, N, Picea excelsa. O, P, Larix 



kaempferi. Q, Pseudotsuga taxifolia. 5, primary suspensor; fj, c^. embryonal tubes; 



r, rosette cells, which may give rise to rosette embryos, re (after Buchholz). 



most derivative type. And between Pinus and Pseudotsuga, genera with 

 embryos showing various intermediate features are known. Fig. 43. 

 This is the basis of the conception advanced by Buchholz in 1931. 

 Until we have more knowledge of the factors involved in the inception 

 and development of the various embryonic features, and some clue 

 as to how these features change under the impact of genetical change, 

 it will be difficult to determine finally the taxonomic relationships. A 

 sufficiently detailed account of the various embryonic conditions in the 



