

1920] CURRENT LITERATURE 165 



his own contribution. He concludes that the apical cell in early embryogeny, 

 cleavage polyembryony, rosette embryos, rosette cells, and the direct organiza- 

 tion of embryo initials from free nuclei of the proembryo are primitive features; 

 while the organization of embryo initials after walls form in the proembryo, 

 a proembryo that fills the entire egg with cells, the archegonium complex, the 

 embryo cap, and the return to simple polyembrony are advanced or specialized 

 features. A study of polyembryony throughout the groups shows that 

 cleavage polyembryony tends to become more or less eliminated in passing 

 from the lower to the higher genera, and consequently the conifers must have 

 been derived from ferns with cleavage polyembryony. 



Chamberlain, 8 in dealing with the Cycads, considered two questions: 

 "What has been their origin ?" and "Have they left any progeny V From a 

 study of the comparative morphology of the entire Cycadophyte phylum, from 

 the Paleozoic to the present time, he concludes that the Cycads could not 

 have come from any Mesozoic forms of the Cycadeoidea type, or from any 

 known forms of the Lower Mesozoic. If they have come from any of the 

 Bennettitales, they have come from forms so nearly like the Cycadofilicales, 

 to which the Bennettitales themselves owe their origin, that whether the 

 Cycads are an early branch from the Bennettitales, or have come from the 

 Cycadofilicales directly, can be answered only by fossils still to be discovered 

 and studied. 



The second question, so far as the living Cycads are concerned, is answered 

 positively in the negative. The groups of living seed plants are considered 

 separately, and the conclusion reached that the Cycads are not responsible 

 for any of them. This conclusion was emphasized by some facts indicating 

 that the Coniferophytes and Angiosperms have a more reasonable origin in 

 the Ferns or Lycopods. Stress is laid upon the fact that the extinct forms 

 which have been preserved are mostly woody, especially in the Mesozoic. 

 Have herbaceous Gymnosperms been lost which may have given rise to her- 

 baceous Angiosperms? Could such Angiosperms have given rise to the 

 woody Angiosperms which became prominent in the Cretaceous? It is 

 difficult to derive these Angiosperms from any known woody Gymnosperms. 

 The general conclusion is that the Cycadophytes have come from Ferns, 

 and that they have not left any progeny outside of the Cycadophyte line. 



Wieland 9 deals first with the distribution of seed plants, almost exclu- 

 sively with fossil seed plants, and then discusses relationships. In living 

 plants, only lateral distribution is considered, but in fossil forms both lateral 

 and vertical distribution must be studied. The vertical distribution, in most 

 cases, is better known than the lateral, and the period of extinction is more 

 determinable than the first appearance. The Carboniferous flora is better 



8 Chamberlain, C. J., The living Cycads and the phylogeny of seed plant? 

 Amer. Jour. Bot. 7:146-153. 1920. 



9 Wieland, G. R., Distribution and relationships of the Cycadeoids. Amer 

 Jour. Bot. 7:154-171. 1920. 



